The cooling tower repair systems are evaluated considering the safety and the improvement of structural strength. Two repairing systems have been ordinary adopted for the old cooling tower. One is adding the concrete layers on the shell surfaces. The other is stiffened by the R/C ring stiffeners. In this analysis, former procedure is adopted and is analyzed by focusing on the effect of the additional thickness. The finite element procedure based on the isoparametric degenerated shell is adopted to evaluate the effects of repairing the old cooling tower. Numerical parameters are the shell thickness and the amount of additional reinforcement. From the numerical analysis, the initial crack load, the reinforcement yield load and the failure load are detected and the safety of the old cooling tower is discussed.