The relationship between response of grain impact sensitive plate in grain loss monitoring sensor and damping ratio was theoretically analyzed, and the importance of damping design in sensitive plate was pointed out. A method to increase the damping ratio of the system was proposed, which could quickly attenuate harmonic vibration of sensitive plate by laying a constrained damping layer on sensitive plate. Through grain collision response test on sensitive plate with different damping loss factor, optimal material and structure of the sensitive plate were determined, and the modal analysis of the sensitive plate was carried out though ANSYS software to find out the best location of constrained damping layer on sensitive plate. Grain collision response test results showed that, the time of grain collision signal waveform decayed to 1.5V was shorten from 10ms to about 3ms before and after partial constrained damping treatment, which proved that the detecting frequency of grain loss monitoring sensor was greatly improved.