Based on the mechanical analysis of the plate-inclined plunger-type hydraulic transformer,a mathematical model describing the instantaneous torque of the fluid-distribution ports is established in the conditions that the control angle is equal or unequal to zero. Then,a simulation is carried out with Matlab,finding that the torque of each fluid-distribution port is discontinuous,and that there exists torque beating between two cycles. Finally,a mathematical model describing the torque-beating coefficient is established,followed by a simulation test. The results show that the torque-beating coefficient varying with the control angle is rather high,which results in the unstable operation of hydraulic transformer.