Abstract:PLC programming usually need to consider the system reliability and practicability, also needs to satisfy its technical requirements, and optimize the program This article withcalculator PLC program for the model, the finite state machine theory knowledge used in the PLC program design, further strengthen the study of S7-GRAPH programming language and understanding.And put forward some of the PLC design ideas and techniques, this method can be effectively applied to the actual control system, advantageous to the system maintenance and extension and modification of the program.