In modem productivity continuously improve, under the situation of the construction of the unmanned air compressor station, is a social development process in the inevitable choice. This paper mainly describes a kind of PLC in nitrogen making machine, the application of PLC in air compressor for automatic control transformation, realize the air separation control and production equipment of centralized control. In transforming the original system based on nitrogen making mechanical and electrical machine, the direct startup control method to frequency conversion control, reducing the impact of the grid system and energy saving, and formulate the concrete implementation control mode, equipment start-stop steps, software function and function expansion, alarm system. And by using the corresponding control algorithm, realize supply of gas supply constant, improve the quality and efficiency, and ensure each work of safety for production.