The GPR wave frequency can reflect the lithology of the strata. The frequency of the electromagnetic wave varies obviously when the electromagnetic wave penetrates through different media. The relationship between the GPR wave frequency and the grade of rock mass is analyzed in terms of rock mass grade, lithology and hydrology condition. Conclusions drawn are as follows: For different grades of rock mass, there are different GPR wave frequencies; The worse the lithology of the rock mass, the lower the frequency; For rock mass of the same grade, the frequency has no obvious variations when the hydrology changes.