In order to study the characteristics of circulating cooling system of LNG plant under shutdown state and find out win-win solution between economy and environmental protection for cold-operation, combined with the control cases of circulating system in LNG plant during shut down, plan has been made by adding and changing chemicals, optimizing circulating water flow, controlling circulating water pump power consumption. Research shows that concentration ratio is a key factor in water treatment. With high concentration ratio, chemicals will stay longer in the water. Persistent chemicals with good stability shall be selected. If at a much lower concentration multiple, adjustments must be made immediately to chemical dosage and types. Circulating water pump flow control must be used with chemical control. PH adjustment is helpful to water treatment and has high potential value for energy saving. PH adjustment can be used in combination with chemical control and flow control to achieve the best water treatment with biggest economic effect.