Ultrasonic rebound testing technology of concrete strength, referred to as "comprehensive method", is one of the nondestructive testing methods of concrete strength. The so-called comprehensive method is to use two or more nondestructive testing methods (ultrasonic pulse velocity-rebound value) to obtain a variety of physical parameters, establish the comprehensive correlation between strength and various physical parameters, and thus comprehensively evaluate the strength of concrete from different angles. Because the comprehensive method adopts many physical parameters, which can comprehensively reflect various factors that constitute the strength of concrete and offset some factors that affect the correlation of physical quantities of strength, it has higher accuracy and reliability than the nondestructive testing methods of single physical quantity (rebound method and ultrasonic method). Single rebound method and ultrasonic method, the same influencing factor has different effects on different methods, and some are even completely opposite. For example, when the concrete strength grade is the same, and the production technology and mix ratio are basically the same, when the strength of standard concrete specimens is tested by single rebound method and ultrasonic method, the concrete age and concrete humidity are found. For rebound method, with the increase of concrete age, the concrete surface hardens, which makes the rebound value higher, while the surface hardness of wet concrete decreases and the rebound value decreases significantly. For the ultrasonic method, the situation is the opposite. With the increase of age, the interior of concrete tends to be dry gradually, and the propagation speed is low, and the propagation speed of wet concrete is faster than that of dry concrete. If the two single methods are combined, the effects of concrete age and humidity can cancel each other out without consideration. In this way, the comprehensive method makes use of two physical indexes that have the least damage to the component, one is to use the physical indexes inside the component, and the other is to comprehensively reflect the compressive strength of concrete from the surface hardness. Because it is the strength index of concrete in many aspects, it has a good correlation. In addition, the comprehensive method has certain advantages over the semi-damaged core drilling method, which is not suitable for large-scale use in structures because it will cause local structural damage to structures or components. In this way, the comprehensive method of "ultrasonic pulse velocity-rebound value" has become an important development method of nondestructive testing technology for concrete strength.