In this paper, an adaptive complementary sliding mode control strategy based on nonlinear extended state observer (NESO) is proposed for the ship course tracking control subject to environmental disturbances. By introducing the adaptive law, the system uncertainty is estimated and adjusted, so that the boundary layer of the complementary sliding mode control can realize dynamic changes and ensure the system robustness. At the same time, the auxiliary control system is introduced to compensate the complementary sliding mode control law to guarantee the system stability under finite actuation. For the environmental disturbances of the heading process, a NESO is designed for real-time estimation and compensated to the adaptive complementary sliding mode control law to improve the robustness of the system. The closed-loop stability is proved, and simulation results show that the control strategy effectively improves the tracking accuracy and robustness of the system.