Abstract: Based on the magnetic particle flaw detection theory and the establishment of physical and mathematical models of mechanics of the spherical magnetic particle in leak field, the effect of various factors including the magnetization current, magnetic yoke probe, etc. in the actual use on the performance of magnetic powder testing instrument was expounded in this paper. Then through improving the magnetization power which was the core part of the magnetization powder testing instrument, the key technology of the magnetic powder testing instrument was offered, which was to select the square-wave produced by frequency inverter as the composite magnetization technology.