For amphibians aircraft, Ground and water handling characteristics should meet the requirements of airworthiness regulations, and an accurate computation analysis method should be established to carry out the evaluation during the optimization design process of the aircraft scheme, so as to ensure the airworthiness compliance of the aircraft scheme and reduce the risk of design change. Based on the planing boats hydrodynamic analyzing methods, landing gear system multibody dynamic modeling technology and Matlab/Simulink simulation environment, a mathematical flight simulation model of flying boat in water was built, as well as another simulation model on the ground. The time history of various motion state variables, undercarriage parameters, hydrodynamic forces of the aircraft are obtained after the simulation. Finally, a contrastive analysis of the taking-off process between the simulation results and expremental data was made. The results showed that the ground and water flight simulation method was consistent with test data of the amphibious aircraft, can achieve the accuracy requirement of aircraft type design. This method has an important theoretical and practical value in evaluating and improving the aircraft designed, as well as in guiding the airworthiness compliance flight test.