<p class="MsoNormal" style="text-align: left; margin: 0cm 0cm 0pt; layout-grid-mode: char;" align="left"><span class="text"><span style="font-family: ";Arial";,";sans-serif";; font-size: 9pt;">In power system filed, to study the characteristics of the gas breakdown is essential and of importance in designing the protection of high voltage system as well as to the power system reliability. Hence, in this paper, the major purpose is to propose a refined mathematical approach based on core finding in rough set method and GM(h,N) method in grey system theory to find the priority of influence factor in gas breakdown. And also created rough set and GM(h,N) toolbox based on Matlab, which to help the complex calculation and analysis. As the result, we not only can get the rank of influence factor in gas breakdown, but also provides a new idea for extension the applications of rough set and GM(h,N) method.</span></span><span style="font-family: ";Arial";,";sans-serif";; font-size: 9pt;"></span></p>