Li Changchun is engaged in the research of optical radiation measurement technology. He is one of the earliest scientists engaged in the study of quantum radiation in the world, and has developed a number of optical radiation measurement standards and instruments, which have filled the gaps in China. In the 1960s, a temporary working standard of color temperature of 2000 K-2854 K was developed, which met the urgent need of calibration of luminosity, chromaticity and integral sensitivity of photodetectors. He developed a standard test device for low light, and proposed a new method (NX 10-6) for measuring extremely low transmittance, which made the L 10-6lx level low light illumination measurement with 5% uncertainty and met the urgent needs of national defense scientific research and production such as night vision low light devices and luminescent materials. In 1970s, the first precision digital illuminometer in China was developed, which reached the level of international similar instruments in V(λ) function calibration, cosine characteristic calibration, linearity calibration, accuracy and long-term stability. In the process of establishing the standard of 500K-1000K total radiation dose, the temperature measurement structure and procedure of the radiation cavity are improved, and the quality of the blackbody radiator is significantly improved, which provides a technical basis for the scientific research and production of infrared guidance and infrared weapon systems in China. From 65438 to 0977, the experimental determination of the maximum spectral luminous efficiency (Km value) was conducted, and the measured value was very close to the average value of Km value measured by nine national standard laboratories in the same period. This work has been valued and praised by the International Bureau of Metrology and the International Advisory Committee on Photometry and Radiosity. In the early 1980s, he used Kr+ and Ar+ lasers, frequency doubling technology and self-calibrating silicon photodiode to measure the amount and output of silicon in the ultraviolet region. The uncertainty is 0.5%- 1%, which is about five times higher than christensen data commonly used in the world. In the future research of "absolute measurement of spectral radiation from 400 nm to 900 nm by using self-calibration technology of silicon photodiode", the dynamic resistance under zero bias voltage is deeply studied, and an effective device pre-selection criterion is put forward in combination with accurate measurement of external characteristic parameters. At that time, it was in the leading position in the world. The scientific research project that Li presided over and participated in won the first prize of national scientific and technological progress twice and won many provincial and ministerial-level scientific and technological awards. His more than 30 research papers have attracted the attention of the international optical radiation metrology community and have a great influence.