Abstract: In order to prevent the tube with low speed water in the open air from freezing in north China, a method by using thermal insulation & electrical heating technology is proposed. Some basic principles of thermodynamics are adopted to study the dynamic character of the water temperature that is under the control of the on-off adjuster. Based on the analyses, specific optimum programs aiming to meet the requirements of different practical conditions were obtained.Results show that this protection method is reliable and the optimum thermal insulation layer thickness is related to the electric price, heating power of electric cable and the price of thermal insulation material.