In order to solve such problem as data instability occurring in cathodic protection system commissioning of a certain natural gas treatment plant, conducted are field test, data recording and comprehensive analysis and, such factors are ruled out one by one as external temperature influence and external power network voltage influence and it is ultimately clear that instable cathodic protection system data result from incomplete cathodic polarization of the protected objects and large size of cathodic protection power supply equipment. Therefore, it is very important to reasonably select size of cathodic protection equipment based on the protected objects in cathodic protection system design and the protected objects shall be completely polarized before cathodic protection system commissioning.