Abstract: Buoyancy method with less equipment and simple control, used in ground demonstration of space operation is presented. Because the model suspended in water where gravity is cancelled by buoyancy force has six degrees of freedom, buoyancy method looks like the best choice for function test of space robots which grasp the float objectives. The interaction of fluid field and the experimental model is analyzed. It is the problem of kinematics and dynamics. Then the problem how to scheme mass and volume for the model balance in any direction is presented. In addition, the drag fore, soar force and additional mass are formulated. A complicated conclusion is given for all questions in buoyancy method including how to make similar scale be 1:1. The theoretical research and experiments show that this method can be used in microgravity test of space operation. For its low cost and high similarity, buoyancy method is of great application significance.

Key words: Buoyancy method, Dynamical analysis, Operation test of space robots, Suspended model