<p>A predefined-time sliding mode adaptive control method (PDTSMAC)for nonlinear system is proposed in the presence of parameters unknown, external disturbances and arbitrary initial values. Firstly, the expected trajectory of the system is extended to the arrival process with characters of predefined-time convergence and the accurate tracking process of completely tracking the desired trajectory, the design principle of extended trajectory is given; Then, an extreme learning machine (ELM) with exponential convergence of external weights is designed to compensate the uncertainties of the system, and a sliding mode adaptive controller with predefined-time convergence is constructed based on a predefined-time convergent sliding mode surface. The stability of the closed-loop system is proved theoretically. The simulation results show that the control strategy can ensure that the construction robot in arbitrary initial state converges to the extended desired trajectory within the predefined-time, and realizes the complete and accurate tracking of the preset desired trajectory, and the trajectory tracking error is less than 0.008.</p>