Similarity principle was applied to obtain the certain conditions of strength similarity among reinforced concrete column and beam under axial compression, and compression with large eccentricity. The theoretical values of the reinforcement ratio and the thickness of concrete cover were derived, and by selecting the thickness of concrete cover of the model on the bearing capacity, the influence of similar errors was analyzed. The analysis shows that the same reinforcement ratio with the prototype is appropriate for the model test in the reinforced concrete member model test. For axial compression column, the thickness of the concrete cover of the model does not have any error. For the reinforced concrete beam, the thickness of the concrete cover of the model takes prototype protective layer thickness divided by 0.5 times the proportional coefficient. The error can be controlled within 10%. For large bias column, it is suggested that the thickness of the concrete cover takes prototype protective layer thickness in addition to scale coefficient.