Abstract: In order to measure the phase displacement of a heterodyne interferometer,namely Doppler frequency shift,an interpolation processing method of the heterodyne interferometer based on field programmable gate array(FPGA)was introduced. Based on zero-crossing detection,it starts to interpolate pulses at the rising edges of measurement and reference signals respectively and the phase displacement can be calculated by counting the interpolated pulses.In the experiment,the light source is He-Ne laser with beat frequency of 2.2MHz,measurement device is Michelson's interferometer,and the inserting pulse frequency is 100MHz.The following calculating work,such as counting,multiplication and division,was accomplished by FPGA.From theoretical analysis,the measurement resolution can achieve,(11)/(1000)λ,about 6.9608nm.The result indicates that is of high value for practical application.