Abstract: According to experiement of high speed photography, we found that the vertical acceleration is always negative value after san particle leaving ground surf ace, there is no upward external force smaller than gravity acting on the sand particle. Thus five out of eight lifting-off hypotheses of noncontacting force were precluded, such as buoyance force hypotheses, differential pressure hypotheses, turbulence hypotheses, negative pressure hypotheses and vortex hypotheses. Of the other three lifting-off hypotheses of contacting forces, the author considered the saltant lifting off as an interactive result between bevel flying and impact. The rolling sand particle which move om uneven surface can detach from ground surface with low velocity(cm/sec)and get more energy from wind. Those sand particles which roll on the surface or fly in the air impact other particles from different angles,and bounce back at a-cute or obtuse angle. If the 10% of kinetic energy of moving sand particles transformed into rotative energy, sand particles could obtain hundreds or more than thousand of rotations/second of rotative velocity.