In order to solve the shortcomings of Fabry-Perot (F-P) interferometer frequency-locking method in terms of response speed, anti-interference ability and long-term stability, a differential frequency-locking scheme of F-P interferometer is proposed. Dual-frequency laser with frequency difference is coupled into F-P resonator. When the laser frequency difference is small enough, the signal curves of two light intensities will cross. Taking the difference between two light intensity signals as the controlled variable, a monotone zero crossing function is constructed near the crossing point, which is used as the feedback of the closed-loop control system to realize dynamic differential frequency locking control. Based on the scheme, a set of F-P interferometer micro-displacement measurement device was built and experimental verification was performed. The results show that the device could realize micro-displacement measurement in the range of 0 ~ 300 nm, and the displacement measurement resolution reached 23 pm, which verified the effectiveness of the F-P interferometer differential frequency-locking scheme, and provided an important reference for the development of micro-displacement measurement.