The AC power system used in substation plays an important role in the core of the substation. Due to the risk of loss of voltage in the whole station during the transformation of the traditional mode, the AC power system will operate safely, reliably and stably for the important equipment such as the DC system, the main transformer air cooling system and the power supply of the remote device, and even cause power outage and equipment damage in the power grid system. In view of the above problems, this paper studies a method for the original screen transformation of AC power system used in substation stations and applies it in practice, providing reference for the subsequent substation AC system transformation projects.