After introducing the status of the APS used in thermal power unit, some reasons for the limited application of the APS in thermal power units at the present stage are summarized . From the perspective of improving the applicability of APS system and making optimization without changing the field equipment configuration as much as possible,as well as the investment effect of APS control system, the two preselected logic of mutual standby equipment and three preselected logic of mutual standby equipment are analyzed.Then gradually optimizes them, reduce the interruption phenomenon in the execution of APS system, and improve the efficiency of unit start and stop. It has a high reference value and significance in the design and implementation of the APS of various types of thermal power unit.