The invention relates to a wave-surface differential interference space light demodulator, and in particular relates to a free space light demodulator of DPSK (differential phase shift keying) signals. The wave-surface differential interference space light demodulator provided by the invention comprises a block polarization beam splitting device, a beam combining device, a reflector and a pupil matching time differential interferometer which comprises two groups of pupil imaging lenses. The wave-surface differential interference space light demodulator provided by the invention is used for demodulating the light signals in a space laser communication receiver; the output data light signals are used for balance detection; and the output position light signals can be used for fine tracking.