Accurate selection of rock mechanics parameters has always been a key scientific problem in geotechnical mechanics and engineering area. To solve this problem， firstly， the parameters of joint spacing and quantitative block volume （Vb） are introduced， and the calculating formula of the geological strength index （GSI） is proposed based on block volume （Vb）. Meanwhile， the calculation formula of the disturbed factor for rock masses （D） based on ultrasonic velocity （Vb） is given. The above GSI value and D value are introduced into the Hoek-Brown strength criterion， and a rock mass mechanical parameter estimation method based on the block volume （Vb） and the ultrasonic velocity （Vb） of the rock mass is proposed. Firstly， the validity of the calculation of the geological strength index （GSI） based on block volume （Vb） was verified by comparing it with the existing GSI calculation method. Then， the estimation method of rock mechanics parameters based on Vb and Vp was applied to the parameter evaluation of Tianxi Expressway. And the numerical calculation results were compared with the field investigation and monitoring results， so as to verify the feasibility and accuracy of the proposed method. This method extends the application scope of the Hoek-Brown strength criterion and provides a new idea for parameter selection in the case of insufficient experimental data at the initial stage of engineering construction.