A second order dynamic terminal sliding mode control strategy is proposed for a class of uncertain non-affine nonlinear systems with input constraint. Firstly, without loss of the accuracy of the model and considering the input saturation, a global approximation method is presented. Then, a disturbance observer based on the wavelet cerebellar model articulation controller is designed in order to ensure the effective approximation for unknown compound disturbances. Subsequently, An auxiliary system is constructed to analyze the influence of the input saturation on the tracking error. In order to overcome the chattering problem in the traditional sliding mode, the design process of second order dynamic terminal sliding mode controller is given by constructing terminal sliding mode surface based on the PI sliding mode surface. Finally, the simulation results show the good tracking control performance of the proposed method.