Transformer is one of the important equipment in power system． The ability of transformer to withstand short circuit plays an important role in the safe and stable operation of power grid． An unqualified test for short － circuit withstand ability of a 110 kV transformer is analyzed． By comparing the test data before and after the short circuit of transformer，the causes of the accident are analyzed from the aspects of design，material and process combined with the disintegration of the transformer． And the targeted rectification measures are proposed at last．