The mathematic models of displacement, flow, angular torque and efficiency about angle type hydraulic transformer were built respectively. Then, the efficiency hill of hydraulic transformer was drawn, and efficiency characteristic was revealed. The results of analysis and test show that the total efficiency of hydraulic transformer is above 70% in normal condition and the high efficiency range is wider. The total efficiency increase first and decrease afterwards with the increment of flow of load circuit or rotational speed, and presents the same change tendency with the increment of pressure of load circuit or rotation angle of valve plate.