Abstract: The launch and takeoff process of spacecraft from Mars is one of the key steps in the mission of Mars Sampling Return (MSR). Based on the Discrete Element Method (DEM), a particle medium model of Martian soil simulant is established to study the bearing behavior of the soil. A multi-factor coupling dynamic model including Martian soil, lander, launcher and Mars Ascent Vehicle (MAV) is also constructed to perform oblique-launch simulation. Results show that the changes in attitude angles of the MAV are relatively small under different launch directions on a slope. The yaw, pitch and roll angles of the MAV are respectively no greater than 1.0°, 3.2° and 0.18° during the launch and separation process. The launch process will affect the magnitude of the bearing load of the Martian soil simulant on each footpad of the lander. However, the lander's pitch angle and sliding distance are small. The overall attitude of the lander is stable, which means the lander can effectively support the MAV's launch process. The research method used in this paper is able to guide the dynamics simulation and stability design of planetary launch devices.