In view of the problem of the braking effectiveness obvious fluctuation,poor system stability of traditional underground transport vehicle,the wet brake is introduced to the traditional underground unmanned vehicle braking system,the calculation and simulation study of the drag torque which is the main evaluation index of wet brake system is carried out,and the change rule of the braking system drag torque under the condition of different oil supply quantity,oil viscosity and groove type is got. The results show that,with the increase of the oil supply quantity of braking system,the drag torque of all kinds of wet brake friction disk model show an increase trend; the influence of the oil supply quantity change on the drag torque generated by radial oil grooves is more obvious than the spiral oil groove and waffle oil groove; under the condition of high speed,the same external condition,the drag torque generated by radial oil groove is obviously higher than that of the spiral oil groove and the waffle oil groove.