A wheel-propeller-leg integrated amphibious robot with multi-modes motion is presented as a new type of robot, which can both crawl on land and swim underwater in certain depth. The performance of swimming with the mixed thrusters composed of wheel-propellers and legs shows its propulsive capability when the robot swims in water. Based on analysis of propulsive principle of the wheel-propeller and the leg, hydrodynamic characters of the mixed thrusters are calculated, and the approximate models for propulsion of the wheel-propeller and leg are obtained according to computational calculation and simulation with commercial software. Considering the feature of energy-taking by itself, the optimal distribution of propulsion based on the wheel-propeller-leg mixed thrusters with the maximal navigational distance is studied using multi-objective optimization theory. As a result, the optimized driving parameters for the mixed thrusters are achieved to bring the maximal propulsion while consuming the minimal energy. Experiments carried out in the pool prove the validity and rationality of the optimization results.