For the uncertain control of manipulator under unknown load, a general method for designing the gain of nonlinear observer was proposed based on the nonlinear disturbance observer and sliding mode control method. By designing an adaptive nonlinear disturbance observer, the uncertainty caused by unknown load of manipulator was approached, and the external force caused by unknown constant load was estimated, and the scope of observer disturbance was extended. Under certain conditions, Lyapunov square method was used to prove the stability of the observer. The simulation results show that the sliding mode control method of adaptive nonlinear observer can be used to effectively alleviate the chattering problem of manipulator control in the control system of nonlinear manipulator with load change.