To eliminate the deviation between the actual pressure and the expected pressure of the shifting clutch of hydraulic mechanical continuously variable transmission (HMCVT) during the pressure tracking control process, a global terminal sliding mode control algorithm based on extended observer was proposed to achieve the high-precision tracking control of the pressure. By establishing the nonlinear mathematical model of wet clutch with uncertain disturbance, the state space equation of pressure control system was derived. The mismatched disturbance was estimated by extended observer, the linear term was introduced to accelerate the global convergence of terminal sliding mode control. Then a global terminal sliding mode pressure tracking controller based on extended observer was designed for HMCVT shifting clutch pressure system in real time. Finally, the effect of the controller was simulated and verified by bench test. The simulation and test results showed that the uncertain disturbance can be accurately observed by the extended observer. Compared with the traditional TSMC, the dynamic response time was only 0.13s, the overshoot was only 0.08MPa, and no chattering phenomenon occurred for the proposed algorithm. In addition, the control algorithm had good performance anti-interference capability, which was reflected by the smallest jerk (reduced by 12.7% at most) and sliding friction work (reduced by 10.2% at most). The results proved that pressure tracking control algorithm proposed had good robustness, and it can be applied to pressure tracking control of HMCVT shifting clutch.