Abstract: Two air compressors of CNPT have been taken the combine-controlled system design.The design schemes are as follows:First of all, makes the air compressor variable-frequency transformation，and then connects two air compressors, frequency changer and master control PLC in the same network via RS-485 bus, and finally designs the process combine-controlled algorithm.And main pipeline pressure and running status of air compressor system have been taken real time monitoring at the same time.Practice shows that this design has realized the two air compressor adjust the output volume automatically and continuously according to the variation of gas load and achieved the goal of voltage stabilization and consumption reduction.