Abstract: The article makes investigation and analyzes the quality of pipeline coating with asphalt in combination with cathodic protection. Major reason affecting pipeline coating's quality comes from external factor, mainly including soil's physical and chemical properties, ambient temperature and current interruption (potentiostat operation coefficient and stray current) etc.. It Is given through study and analysis that the quality of the coating in more water content area along the pipeline is superior over that of less water content and increasing ambient temperature around the pipeline will accelerate aging of coating, therefore the coating at outgoing section will be serious aged than that of incoming section. When intersected with electric line, the coating of the pipeline will be aging due to secondary voltage inducted.