The S7-200 of PLC of the Siemens to realize the check of the safety belt usage life-span is introduced.The system is made up of A and B two set of function quite same subsystems.Each one is made of solenoid valve,air cylinder,position signal,six shuttles fraction columns.The core of the system is the PLC.Part of the organic combination of the safety belt system to is made complete the safety belt usage life-span check.The work principle and the control process are emphatically elaborated.