Abstract: In order to study the oil discharging features of the parking brake,based on the structure and working principle of the parking brake applied to the light type flame proof rubber tyre vehicle,the mechanics stress balance and the flow continuity principle were applied to establish dynamic mathematic model of oil discharging proce ss. With numerical calculation of model,feature curve of oil discharging process was obtained for the parking brake. The paper provided several structure parameters sensiti vely to the oil discharging features and had studied on the influence law.The results showed that with reduction of orifice area in the valve port of the reversing valve,the oil discharging time would be increased obviously.With reduction of the spring rigidity,the oil discharging time would be extended appropriately,but the oil hydraulic pressure re quired to release the braking would be reduced.With a piston area enlarged,the oil discharging time would be increased obviously and the oil hydraulic pressure required to release the braking would also be reduced obviously.