Abstract: In order to evaluate the cathodic protection level of a pipe section,it is necessary to measure its Off-potential,The measuring methods of On Off-potential are introduced,The measuring results of On Off-potential in Northeast Oil Pipeline Networks showed that the given potential values of the potentiostat were generally lower at a certain extent.If Off-potential criterion at -850 mV(vs.CSE) was used to judge the level of cathodic protection,only 65% of measured pipe sections would be fully protected,while 23% of measured pipe sections can be considered to be well protected if 100 mV polarization criterion will be used to evaluate the cathodic protection of those pipe sections,The On-potential values regularly changed along the pipe section,while the change of its Off-potential values did not appear significant tendency,The results also illustrated that the degree of coating degradation was the main factor affecting IR drop,The cathodic protection potential was an important parameter in pipeline's anti-corrosion system,Off-potential was clearly reflected whether the pipeline was fully protected or not,while the distribution of On-potential reflected both the state of cathodic protection and the degree of coating degradation,If proper technology reform were carried out,about 97% of pipe sections in Northeast Oil Pipeline Networks would be fully cathodic protected,However,there is no mature solution to those pipe sections(about 3%) suffering the stray current interference.