Abstract: To study the effect of temperature on the ultrasonic detection of screw fastening force, an experimental study of screw fastening force detection method is carried out on the MJ45 screw of the cable clamp of the Longmen Bridge. Firstly, a single screw model is made in the indoor environment laboratory, and the screw is tensioned to different stress states by using intelligent tensioning equipment, and the environment temperature is adjusted. The relationship between ultrasonic echo time and screw fastening force under different temperatures is studied by using ultrasonic longitudinal wave detection method, and the ultrasonic detection formula for screw fastening force is established. Secondly, a cable clamp model with 8 screws is made, and all screws are tensioned to the design value. Based on the ultrasonic echo time value and the single screw fastening force detection model, the fitting values of screw fastening force are obtained by interpolation method, and compared with the actual effective fastening force of the screw. Finally, the ultrasonic detection formula for screw fastening force is corrected based on the experimental results. The results show that temperature has a significant effect on the ultrasonic echo time, but at different temperatures, the difference in screw stress results in the same difference in echo sound time, that is, the echo sound time difference is not affected by temperature and the slope of the relation ship between echo time and screw tension is 3.934 5×10⁻³ μs·kN⁻¹. In the full-scale test, the maximum deviation between the ultrasonic fitted screw tightening force of a single screw and the actual screw tightening force is about 16%, and the correction coefficient of the ultrasonic testing formula is finally proposed to be 1.12. The research results can provide a basis for the detection of screw tightening force in actual engineering.