The invention discloses a braking system of a hydrostatic transmission vehicle and a braking method. The system comprises an ECU (electronic control unit), an engine/motor, a hydraulic pump, a hydraulic motor, a hydraulic valve, a braking pedal, an electromagnetic clutch, a hydraulic pump A/B port pressure sensor, a motor revolution speed transducer and the like. Different from an existing braking method of the hydrostatic transmission vehicle, the method which produces braking force positively related to the opening of the braking pedal by using characteristics of a hydrostatic transmission system during braking is provided innovatively. With the adoption of the method, the braking effect of traditional mechanical braking vehicles can be realized without assistance of a mechanical braking system, problems of vehicle sudden stoppage impact, short sliding distance or uncontrollable sliding parking positions of existing hydraulic transmission vehicles during braking can be effectively solved, and man-machine controllability and usability of the hydrostatic transmission vehicle are enhanced.