A parallel type hydraulic retarder with a clutch device and a separation method thereof relate to a parallel type hydraulic retarder with a clutch device and a separation method thereof. The hydraulic retarder used for auxiliary braking produces a certain power loss, which increases the fuel consumption of the vehicle and reduces the economical operation of the vehicle. When the hydraulic retarder is not running under braking, there are residual residues in the working chamber. and a small amount of working medium that meets the requirements of the lubrication and cooling cycle, which increases the idling loss of the hydraulic retarder, and the idling loss will generate corresponding heat problems. It includes the brake shaft, the first control system, the sleeve gear clutch, Speed-increasing gear shaft, speed-increasing gear, friction clutch, friction clutch actuator, second control system, hydraulic retarder rotor, stator, hydraulic retarder control liquid filling mechanism, transmission output shaft, transmission gear, brake A moving shaft bearing, a gearbox output shaft bearing, a first control valve, a second control valve and a housing are invented for use in the field of heavy commercial vehicle braking.