This paper studies the short impedance of 1 500 MVA/500 kV large capacity transformer. It shows that to reduce the short-circuit current of large capacity transformer， the short-circuit impedance should be increased with the capacity. Because the reactive power loss is proportional to the short-circuit impedance，the reactive power compensation should be increased correspondingly， and the voltage fluctuation on the middle voltage side and low side of transformer increases as well. According to the characteristic of the high short-circuit current of the Pearl River Delta power grid， this paper also studies the short-circuit impedance of 1 500 MVA/500 kV large capacity transformer on the short-circuit current and reactive power compensation of the 500 kV Shuixiang Substation. The parameters for 1 500 MVA/500 kV large capacity transformer in Guangdong power grid are recommended.