Abstract: A full ocean depth landing vehicle is proposed to meet the requirements of large-scale mobile investigations and precise fixed-point operations on the seabed. A landing vehicle with two-stage ballasts is designed to improve the diving-floating motion performances and solve the problems of the loading parameters and the diving-floating time. The drag, lift and tilting moment of the landing vehicle are calculated by ICEM and Fluent hydrodynamic analysis software based on the dynamics and kinematics analysis model of the landing vehicle during diving and floating motion, the loading parameters and the position of the center of gravity. The hydrodynamic parameters are identified by the least squares method. Eventually, the mathematical model of the diving-floating motion performance and the loading parameter is established. The diving-floating speed and posture of the landing vehicle are controlled by adjusting the mass and position of two-stage ballasts, and then the motion performance and the time of the diving-floating process are studied and optimized. The analysis results show that the shortest diving and floating time of the landing vehicle are 5.39h and 5.98h respectively, when the primary and secondary ballasts are 53kg and 50kg respectively, and the installation positions are 0.38m and 0.58m respectively. After optimizing the loading parameters, the landing vehicle has the best diving-floating motion performance and can complete diving-floating motion in the shortest time, which provides more time for scientific research and operation on the seabed.