In this paper the figure influence function of deformable mirror is discussed.In view of that the most useful wave front sensing methods are based on measuring the wayefront slopes, we propose to measure the slope influence function, by using which the wave front reconstruction matrix is composed. The method of measuring influence function of deformable mirror by digital interferometer is introduced. From the measured data, several parameters of influence function such as coupling, Gauss exponent and characteristic width can be obtained. The interferomtric results of slope influence function are compared with the measuring data from a H-S sensor.