In this study, an adaptive modified reaching law-based switch controller design was developed for robotic manipulator systems using the disturbance observer (DO) approach. Firstly, a standard DO is employed to estimate the unknown disturbances of the plant, from which the control signal could be compensated. Then, an adaptive modified reaching law is established to dynamically adapt the switching gain of the sliding mode robust term and further guarantee the finite-time arrival of the established sliding surface. Additionally, the convergence of the error system is analyzed via the Lyapunov method. At last, the feasibility and effectiveness of the proposed control scheme are verified by using a two-joint robotic manipulator model. The simulation results show that the developed controller can achieve rapid tracking, reduce system chattering and improve the robustness of the plant. The main innovations of the work are as follows. 1) A new adaptive reaching law is proposed; it can reduce chattering effectively, and it has a fast convergence speed. 2) Regarding the nonlinear robotic manipulator model, a novel adaptive sliding-mode controller was synthesized based on the DO to estimate the unknown disturbance and ensure effective tracking of the desired trajectory.