Vibrations influence normal and stable work of gear pair. In gear pair design process, inherent frequencies of gear pair should avoid working frequencies. Vibration analysis is made on the gear pair of SP-I-01 hydraulic top drive drilling system, the first 6 order inherent frequencies and the corresponding mode shape graphs of the gear pair have been obtained. The maximum operating frequency is calculated and by comparing with the inherent frequencies of the gear pair, the result is that the maximum operating frequency is lower than the inherent frequency of the lowest order, which meets the design requirements.