Aiming to clarify the efficiency characteristics of the closed-loop hydrostatic system with variable pump controlled variable motor, the combined theoretical and experimental approach was adopted to systematically investigate the efficiency performance. The lumped resistance parameters were employed to characterize the system losses, based on which the system efficiency model was established. Through an experimental platform, the characteristics of each resistance parameter in the model were identified. Based on the established efficiency model, the variation laws of system parameters such as slip, torque loss and efficiency with load were predicted, and the validity of the model was verified by experiments. Meanwhile, the influence of oil temperature on the system efficiency characteristics was explored. The results showed that the established model can effectively characterize the drive efficiency of the system. When the load torque was with the range of 20 ~ 40 N·m, the sequential displacement adjustment strategy can achieve the highest drive efficiency, up to 55% . In addition, within the oil temperature range of 40 ~ 70℃, the system efficiency under pump control was increased with the rising of oil temperature, whereas under motor control, increasing oil temperature reduced the system efficiency, and the reduction magnitude became significantly larger with the increase of motor speed. The research result clarified the efficiency characteristics of this type of hydrostatic drive system, providing theoretical reference and engineering support for designing appropriate control strategies and achieving optimal driving performance.