Abstract: Recently, many thermal power unit is put into service.Those thermal power units, especially supercritical unit, have high operating parameters, complex process system, various high equipment. Those characters put forward higher request to automatic control system. Making Full rational use of the automatic control system is a key method to operate equipment safely, reduce energy consumption, improve the economic benefit in thermal power plant. In this paper Automatic unit start-up and shut-down system (APS) of thermal power unit is introduced in detail, and put forward switch control strategy design method of whole process, full condition, automatic control system. Finally, the paper gives application case of whole process, full condition, automatic control system. switch control strategy design method of whole process, full condition, automatic control system. This switch control strategy design method is proved to be effective by application case.