Glass fiber reinforced composites are widely used in storage tanks for corrosive liquids such as hydrochloric acid. In order to solve the leakage problem of a certain factory’s storage tanks. The type and failure region were located through investigation, sampling, and mechanical testing. By considering the specific conditions, a boundary equivalent model was proposed and derived from the theory of plates and shells. It can locate and measure the cause of failure accurately, without complex numerical modelling process. By focusing on the three key parameters that can avoid failure, the tank design was optimized and the bending stress in the failure region was reduced by 43% without changing the production cost and anti-dumping ability.