The invention discloses a device for measuring stirring loss caused by a high-speed rotating element of an axial plunger pump/motor. The device mainly comprises a main shaft, a cylinder, a torque rotation speed sensor, screws, plungers, a swash plate, a variable rod, a variable piston, a compression spring, a front end cap, a rear end cap, a casing and the like. According to the device for measuring the stirring loss, almost all factors influencing the stirring loss in the pump/motor are taken into consideration, interference of other power loss sources in the pump/motor to measurement of the stirring loss is eliminated through application of proper enlargement of a fit clearance, fastening of a mounting structure and grease lubrication of a bearing, dynamic balance of the rotating element is realized through the designed screw structure, and the stirring loss is measured according to a torque difference measured when a casing is full of oil or devoid of oil under the same work condition. The device is simple and reliable in overall structure, parts are convenient to replace, and the machining and detection costs are low.