The main cable diameter of self-anchored suspension bridge is small and the vertical span ratio is large. In order to study the influence of the pre-tightening force loss caused by creep relaxation of the main cable clamp on the safety of the whole bridge，this study took the main cable clamp of Sanchaji Xiangjiang Bridge in Changsha as the research object, and obtained the empirical formula of the main cable creep changing with initial stress and time based on the metal time hardening creep theory. Considering the influence of radial shrinkage caused by the creep of the main cable and the aging relaxation of the pre-tightening force of the high-strength bolts, the calculation formula of pre-tightening force loss of the high-strength bolts in the cable clamp of the self-anchored suspension bridge during operation was obtained, and the fine finite element model of integration of the main cable and the cable clamp was established by ANSYS for verification. The verification results show that the solution of the calculation formula is slightly larger than the numerical solution by 10~20kN, and the fitting accuracy is good. Therefore, the empirical formula can provide reference for the detection and reinforcement of the pre-tightening force of suspension bridges.