Abstract: In the process of deep-sea lander dive， due to the influence of ocean currents， the sitting bottom position will deviate from the drop point. In order to solve the problem of trajectory deviation of deep-sea lander due to uncontrolled state， a type of lander with dual rudders is proposed， which can be landed accurately with high efficiency and low energy consumption. Taking the deep-sea lander with dual rudders as the research object， the dynamics model of the lander is established by simplifying the system to a certain extent. Based on the Matlab platform， the simulation and analysis method of the dive process of the deep-sea lander is established. Matlab Simulink environment is used to simulate the dive process of the deep-sea lander， and the effects of the rudder size and rudder deflection angle on the dive speed and trajectory of the lander， as well as the effects of the rudder size on the stability of the lander， are analyzed in order to determine the specific size of the rudder. The median theorem is used to change the system's non-affine dynamics equations into affine dynamics equations， and a hierarchical sliding mode controller is designed to track the pre-designed linear and S-shaped paths in response to the underdriven nature of the system， which achieves good results.

Key words: deep-sea lander, rudder, dynamic model, hierarchical sliding mode, path tracking