The waterproof pressure and assembling force of the sealing gasket under steel apparatus and the concrete apparatus are studied by the theory of elasticity, so as to study the difference of the sealing gasket performance under apparatus with different materials during waterproof test. The waterproof test is carried out on the sealing gasket under steel apparatus and concrete apparatus by taking commonly used ethylenepropylenediene monomer (EPDM) gasket for example. And then the relationship between the assembling force and the opening amount and that between the waterproof pressure and the opening amount under steel apparatus and concrete apparatus are studied. The testing results indicate that: 1) The vertical stress of the sealing gasket under steel apparatus is larger than that under concrete apparatus which lead to the higher waterproof pressure of the sealing gasket under steel apparatus. 2) The curve of assembling forceopening amount and that of waterproof pressureopening amount obtained by the two apparatuses are quite similar. 3) The opening amount should be reduced by a certain value when using the steel apparatus instead of the concrete apparatus. 4) The concrete apparatus should be used in the waterproof pressure test as many as possible. 5) The test data should be translated when using the steel apparatus instead of concrete apparatus.