Abstract: SECT is an electric heating technique which has appeared in the world recently. It is of such merits as of simple structure, safety and reliability, high utilization ratio of heat energy and automatic control. This method has already been widely applied to heating insulation of oil pipelines and sticky oil tanks abroad. Since 1970s, some units in China have plunged into experimental research in this way, also for insulation of oil pipelines. Based on the theory of electric maguetic field, the article make a theoretical analysis in detail of SECT, inducing from it the depth of electric osmose in the heating pipes, a. c. impedance, power factors, current leakage and the equations for calculating the definite leakage voltage, as well as its application in design and calculation. It can be seen through practice that to reduce leakage voltage and facilitate construction, heating pipes may be welded directly to the pipeline or oil tank that needs heating.