In order to improve the efficiency of cable force measurement in the long-span cable-stayed bridge, a cable force measurement method based on the microwave interferometric radar is proposed and the measurement results are compared with those of JMM-268 and DaspBCF. Firstly, the displacements of cables of the bridge were measured by the IBIS-S radar system. Then, based on the collected displacement information, fast Fourier transform (FFT) algorithm was adopted to obtain the frequency spectrum as well as the fundamental frequency of the target cables. Finally, the forces of multiple cables were identified by the oscillating frequency technique. The test results show that: the dynamic information of multiple cables can be measured by the microwave interferometric radar simultaneously with high efficiency; test method that transmits the radar wave from bottom to top can greatly avoid the influence of noise; relative errors between the cable forces calculated by data measured with radar and conventional accelerometers are less than 2.2%, which proves that the test results are reliable. The cable force measurement method in this paper is of high efficiency and easy to operate, which is worth promotion.