In inland waterway transportation, ships often experience incidents such as groundings and other navigational accidents as a result of failing to adhere to safe sailing speed. An adaptive controller for ship speed is designed under the dual constraints of water depth and tidal time when entering the port by tide. First, the factors are identified that affect the safe speed of ships and the Barrass II formula is introduced to determine the relationship between ship subsidence and maximum safe speed. Second, a 4-DOF ship motion model is established, and a dynamic safety speed constraint framework is constructed based on requirements such as ship speed, ship posture, Under Keel Clearance (UKC) and tidal time. Finally, dynamic constraints and nonlinear model predictive control (MPC) methods are combined, safety speed constraints and minimum speed constraints are designed, and a speed adaptive control model is established. The experiment shows that the controller can effectively track the target trajectory under the constraint of safe speed, the objective of safe navigation is achieved.