Abstract: Lathe as a kind of metal cutting machine tools is widely used. Traditional lathe adopts relay-contactor control, using many hardware connection devices, reliability poor, and high fault rate and troubleshooting tedious, maintenance time is long, and the production efficiency is not high. With the development of the industry, the control system needs to be optimized. Taking the horizontal lathe CA6140 as an example, its control system using the PLC to be optimized, using frequency converter instead of mechanical governor box to variable frequency speed regulation of spindle motor, for the convenience of troubleshooting, fault self-diagnosis to frequent breakdown of the device. Experimental results show that the control system can meet the control requirements of lathe, reduce the failure rate of the system and its fault self-diagnosis can accurately locate the fault components, shorten maintenance time.