The shunt tripping circuit is installed in AAT for three main transformer substation with four segments. After the AAT triggers, it can achieve load balancing between two transformers with the tripping function. The existing shunt-tripping-circuit has defects in the mode of grand operation. When the AAT isn’t disabled, the operation of remote control cannot be used, and it may cause loss of power station 35kV substation half when the upper Substation is in the shutdown completely. Therefore it needs to be improved and perfect the shunt tripping circuit. In this paper, the principles of AAT in a 35kV substation are analyzed, and the existing defects in shunt tripping circuit are elaborated. Three kinds of improvements are presented at length, which can perfectly solves the problems with existing shunt tripping circuit in AAT.