Abstract: Reasonably defining reinforcing rings for metal tanks is important in avoiding less stability of tank shells so as to guarantee safe operation. Analysis is done in the paper of the allocation of reinforcing rings at present. Based on the inadquacy existing in reinforcing ring design. and accidents caused by tank shell disstability which have ever occured, the writer thinks it necessary to deduct the corrosion margin value during the disign of tank shell's teinforcing rings so that the tank shells can be kept stable enough when the cortosion margin is used up. Also suggested in the paper are the allocation location and number of reinforcing rings. According to the strength requirement of a certain tank, the reinforcing ring design basis should be the deducted value which is the minimum corrosion margin in each reinforcing ring plate. Corrosion margin is related to the factors of service life of a tank. corrosion rate etc. the range of corrosion margin should be enlarged so as to maitain tank shell stability during the operation and main tenence. Corrosion margin is suggested to be no less than 1.5mm as the minimum.