Abstract: In view of the safety problem that rubber-tyred drilling rig should be braked in the emergency of underground transfer site, the working principle of the brake system is analyzed, and the redundant design concept is adopted, a kind of full hydraulic wet brake system is designed from the aspects of hydrostatic closed brake system and mechanical wet brake, which makes the brake system meet the requirement of bad working condition. At the same time, aiming at the problem of the instability of the parking brake pressure, the analysis and calculation are carried out, and the accumulator group is optimized to achieve the goal of safe parking. The test results show that the whole system has the advantages of high parking torque, stable release pressure, safe and reliable braking performance, quick response, and braking distance less than 8 m, which effectively solves the safety problem of emergency braking when the rig is moved.