In this paper, a novel trajectory tracking control method for manipulator task space containing mismatched uncertainty is proposed. This paper considers the mismatched uncertainty that exists in the signal conversion between joint space and task space in the robotic arm system. The time delay estimation is employed to approximate the dynamic and kinematic parameters of the system to achieve model-free control. The time delay estimation errors is treated as part of the system disturbances and a disturbance observer based on an auxiliary control system capable of estimating both matched and mismatched disturbances is designed, which does not require additional design of adaptive laws to compensate for disturbances or upper bounds on the derivatives of disturbances. We transform the control error by a prescribed performance function to accomplish transient control of the error, and design a fast terminal sliding surface for the virtual control variables based on the backstepping design method to improve the convergence speed of the controller. Based on the Lyapunov criterion, the closedloop stability of the whole system is demonstrated. The feasibility and superiority of the method in this paper is demonstrated by numerical simulation compared with other control methods.