In order to improve the global convergence rate of traditional second-order terminal sliding mode control, a fast second-order terminal sliding mode control algorithm is proposed in this paper.Compared to the traditional second-order terminal sliding mode control, a new second-order approximation law is designed with absolute value functions hidden in the integral term, also a linear term is included to improve the global convergence rate.A second-order approaching rule is initially used with the possibility to avoid singularity via parameter tuning until the state has reached the sliding manifold, then a continuous exponential approaching rule is adopted instead to guarantee finite time convergence.Lyapunov direct method is used to prove the stability of fast second-order terminal sliding mode control algorithm and has better convergence properties than that of the super twisting algorithm.A lower extremity exoskeleton is taken as the research object, and its dynamics model is established.The algorithm is applied to the attitude control of the lower extremity exoskeleton with modeling errors and additive disturbance.Simulation results show that the proposed control algorithm can effectively alleviate the chattering effect, and outperforms than that of the super twisting algorithm, which verifies the effectiveness of the proposed algorithm.