Abstract: To address the attitude instability caused by external disturbances during the cross-domain mode transition of a land-air amphibious platform, a hybrid stability control method based on the coordinated action of ground travel and aerial flight was proposed. Through a comprehensive analysis of the dynamic characteristics during ground travel, aerial flight, and the land-air cross-domain process, an integrated land-air amphibious dynamic model was constructed. Considering typical disturbances encountered by the land-air amphibious platform during cross-domain mode transitions, an optimal controller based on the Linear Quadratic Regulator principle was designed. Building upon the ground control method, flight control was introduced to achieve coordinated control of the ground-flight mechanisms. Simulation tests of the cross-domain process for the unmanned land-air amphibious platform were conducted. The results show that, compared with traditional control methods, the proposed land-air cooperative control method significantly improves control effectiveness and enhances system stability.