Abstract: There is insufficient short-circuit resistance of main transformer in old substation in remote mountain area, so it is necessary to make emergency disposal plan on site. Especially easy to produce thunderstorm, hail, wind and other towns, power grid supply risk is quite large. If the substation's main transformer short-circuit resistance is insufficient, then when the power supply lines are hit by heavy rain, it may lead to line switches do not move over the stage to the main transformer switch trip a large-scale blackout accident. However, the short-circuit current in the fault may exceed the designed capacity of the transformer. In this paper, an operation strategy is proposed for the short-circuit capacity of the main transformer。