The 25K bus was designed and manufactured by various bus factories in 1996 according to the requirements of the Bidding Document for Railway Passenger Cars and the Unified Scheme for 25K Bus Cars issued by the Ministry of Railways. This is because the original 25B and 25G passenger cars were not enough to meet the needs of the first large-scale speed increase of China Railway in June 1997. The 25K bus is developed on the basis of the 25Z quasi-high-speed bus, and "K" is the first letter of Kuai (Chinese Pinyin: KuaiSu). The construction speed of 25K passenger car is 160km/h, and new technologies such as full side bearing support, air spring suspension technology, disc braking technology, anti-skid device, lateral control rod device and anti-roll torsion bar device are applied. The air source is double-tube, and the braking device is very different from ordinary passenger cars. The unit braking mode is mainly disc braking, supplemented by tread braking, to ensure that high-speed trains stop within the specified distance. The design life of 25K bus body is 30 years, which improves the interior grade. 1997 won the first prize of national science and technology. 1998 A few 25K passenger cars belonging to Wuchang Depot of Zhengzhou Railway Bureau are temporarily changed to DC600V power supply mode, so that they can receive locomotive power supply. These trains are the first batch of railway passenger cars in China that use DC600V locomotives for direct power supply. They were originally used for K79/80 times from Beijing West to Wuchang, but due to the immature technology at that time, the power supply voltage of these vehicles was unstable in actual use, so they left the factory. At present, these 25K DC bullet trains are still in operation, which are used for K8084/8085 and K8086/8083 trains from Wuchang to Jingmen.

The 25K passenger car is equipped with hard-seat car (YZ), soft-seat car (RZ), hard-seat car (YW), soft-seat car (RW), dining car (CA), air-conditioning generator car (KD), luggage car (XL) and various double-decker buses, as well as special test car and track inspection car. The first express train of Beijing-Guangzhou Railway has increased by 60 trains. The production of China Railway 25K bus started at 1997, and 326 buses were purchased by tender for the first time. By the end of 2000, there were about 2700 25K buses. The production units are Changchun Railway Passenger Cars, Tangshan Railway Passenger Cars, Qingdao Sifang Locomotive and Rolling Stock Factory and Nanjing Puzhen Vehicle Factory. 25K passenger cars adopt 206KP bogies (K stands for air spring and P stands for disc brake), 206WP bogies (used for air-conditioned generator cars and W stands for no rocking platform), CW-2B bogies, CW- 1B bogies and 209HS bogies (improved by Puzhen Factory on the basis of 209PK bogies). In practical application, it is found that there are defects in bogie design. The bogies and car bodies of 25K passenger cars have been improved many times in the years of production, such as the closed plug doors, inverted windows and sealed windshields. By 2003, the new 25T passenger car (BSP was first produced) began to be put into production, while the 25K passenger car was also discontinued at the end of the same year, but it was still widely used in the underbody of China Railway Express trains appearing in various parts of China.

In addition, the 3 1 passenger car of North Korea Railway was manufactured by China CSR Qingdao Sifang Locomotive & Rolling Stock Company on the basis of the 25K passenger car of China Railway, and the car body painting is the same as that of the 25B passenger car of China Railway. It is used for the formation of K27/28 train from Beijing to Pyongyang, but the passenger car attached to the rear of K27/28 train is actually a 30-type passenger car made on the basis of 25G passenger car. In order to meet the passenger flow of short and medium-distance intercity express trains, Nanjing Puzhen Vehicle Factory and Changchun Rail Bus have successively developed 25K double-decker hard-seat car (SYZ), double-decker soft-seat car (SRZ) and double-decker dining car (SCA), which were first used on the Beijing-Shenyang Beijian112 train (* *). On April/8, 2007, the train T112 from Beijing to Shenyang stopped, and the train T53 17/8/9/20 from Shenyang North/Shenyang to Jilin later used two sets of double-deck 25K carbody. The products of Puzhen factory account for most of the double-decker 25K buses, while the output of Changchun factory is not much. The characteristic of the double-deck 25K car in Changchun Factory is that the door is located between two bogies, and the position is low to adapt to the environment of low platform. There are only two kinds of hard-seat cars and soft-seat cars, while the design of Puzhen Factory is standard two-end doors, and a 25K double-deck sleeper bus has been produced. 25K double-decker sleeper bus is a medium and long-distance air-conditioned double-decker bus developed by Nanjing Puzhen Vehicle Factory during the Ninth Five-Year Plan period. There are two types of buses: double hard sleeper (SYW) and double soft sleeper (SRW), but the output is not much.

In addition, the double-decker carriages of the second and third trains of Health Express are also developed on the 25K double-decker bus.