The invention discloses an instantaneous cable force calculation method for a cable-supported bridge based on synchronous compression transformation. The method comprises the concrete steps: determining the basic mechanical parameters of the cable structure such as the nominal cable length and the linear density of the cable and collecting the acceleration response signal of the cable vibration; preprocessing the acceleration response data; calculating the short-time Fourier spectrum of the acceleration vibration response data and extracting the instantaneous frequency ridges by synchronous compression transformation; and extracting the frequency peak and calculating the current time-varying cable force by using the functional relationship between the frequency and the cable force. The method can be used for analyzing the vibration response signals of the bridge cable structure and then monitoring the change of time-varying cable force in real time. Compared with the traditional cable force calculation method, the time-varying cable force can be monitored in real time under the condition of single acceleration sensor and low sampling frequency, the existing engineering situation can be met, the reference can be provided for performance evaluation and life prediction of the cable structure as well as the over-limit early warning of the cable structure and the cable maintenance of the cable-supported bridge can be effectively served.