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.