In the Liangang No.3 Steel Plant, the water level in the cooling water recycling tank was adjusted by manual observation and manual operation of pumping and regulating valves. There were many problems with the control of water level in this way. In light of these problems, technical renovation was carried out, and an automatic control system was adopted for water level control, which consisted of water level sensor, water level regulator, PLC controller, frequency conversion based speed regulator. Ever since the technical renovation, the system has been in good working condition, which not only cut down breakdowns, but also saved power, leading to remarkable economic gains.