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　and　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.