Abstract: The internal corrosion mechanism of oil tanks is analyzed in the light of tanks corrosion in Changqing Oilfield. It is considered that the tank bottom is prone to electrochemical corrosion due to the considerable chlorions, sulfate reducing bacterias, and the certain amount of carbon dioxide as well as hydrogen sulfide existing in the water deposited at the bottom, while oxygen, water vapour and hydrogen sulfide as well as effect of temperature play a leading role for the gaseous phase corrosion on the tank roof.The cathodic reaction for the two kinds of corrosion are all the process of oxygen depolarization. 'Through site investiga- tions and laboratory analysis, a new anti-corrosion technique is put forward and it is suggested to 1. apply corrosion resistant coating material for the surface coating; 2. employ spray derusting and mechanical spray-on methods in the operation within the tank.