Abstract: Elaborated in the paper is the automatic steel pipe length-measuring system composed of hydraulic cylinder，correlation photocell，incremental encoder，Siemens PLC and Siemens FM350-1 high speed counting module. Also briefed is the application of the FM350-1 high speed counting module to the automatic steel pipe length-measuring system. During steel pipe length-measuring process，the said counting module is capable of capturing hi-frequency pulse signals as sent by the encoder，and performing single pulse counting，and accordingly，making accurate measurement of steel pipe length. Thanks to the length-measuring system，failure rate of the equipment is significantly reduced. The system also possesses such advantages as high stability，high automation level，enhancement of productivity and reduction of operation costs.