In this paper, magnetic-resonance based wireless energy transfer technology is used, which employs two coils and realizes energy transfer by magnetic coupling between two coils. Because no magnetic materials are adopted, the cost would be low, and bulk and weight of the whole energy transfer system would be suitable for light equipment's charging. System structure of wireless power supply device for small mobile equipment is built. Based on building magnetic coupling model, the influence of position and load on energy transfer is analyzed according to the equipment's running characteristics, and the results have been validated by the test.