To accurately describe the power transmission in the hydraulic power take-off (HPTO) system, a high-precise model for the HPTO system of a raft-type wave energy converter is presented. The model incorporates all the necessary dynamics and the undesirable physical effects, such as pressure drop, flowrate leakage, flow resistance, and friction. The model is validated by the comparison with the results obtained using a hardware-in-the-loop test rig and results show that the proposed model can describe the power transmission more accurately than previous models. Furthermore, the research focuses on the holistic performance of the HPTO system including the transmission efficiencies of HPTO components, the overall transmission efficiency of HPTO system and the power losses of HPTO components across a wide range of wave parameters. Results show that the power losses from each component and the efficiencies of the hydraulic cylinder and the generator increase as wave height increases or raft length-to-wavelength ratio approaches the optimal value, while the efficiencies of the check valves and the pipeline display inverse variation tendencies. Besides, the hydraulic motor is the main contributor to the overall power losses and the HPTO efficiency displays a similar variation tendency against wave parameters with that of the hydraulic motor.