The invention belongs to the technical field of retarders, and discloses a hydrodynamic retarder rotor. The hydrodynamic retarder rotor comprises a rotor disc and a plurality of blades, and the rotor disc comprises a disc body and a middle shaft connected to the disc body; the blades are evenly distributed around the circumference of the middle shaft, each blade comprises a fixed piece part and a rotating piece part, the fixed piece parts are fixedly connected to the disc body and extend in the radial direction of the disc body, the rotating piece parts are rotationally arranged on the disc body, the blades have a working state and a loss reduction state, in the working state, the rotating piece parts and the fixed piece parts abut against each other and are coplanar, and in the loss reduction state, an included angle is formed between each rotating piece part and the corresponding fixed piece part. In the working state, the fixed piece parts and the rotating piece parts form the unfolded blades, at the moment, the acting area of pressure oil on the blades reaches the maximum, and large braking torque is generated on the blades; and when no-load occurs, the blades are adjusted to be in the loss reduction state, the included angle is formed between each rotating piece part and the corresponding fixed piece part, the bent blades are formed, the acting area of pressure oil on the blades is reduced, and therefore the effect of reducing no-load losses is achieved.