Abstract: The design for the stress discontinuous region in concrete members mainly bases on the experience or requirement of construction in China. It inevitably affects the design quality of concrete. Nowadays, the design method for the concrete stress discontinuous region is based on strut-and-tie model theory in overseas. Concrete design codes for strut-and-tie theory have been adopted by many countries. But there are no quantification indices for the rationality of strut-and-tie models. Bases on the principle of minimum complementary potential energy, propose to take the factor of a complementary potential energy deviation as the quantification index of the rationality of strut-and-tie models. In order to verify the feasibility of the quantification index, take a corbel and a deep beam as examples, the reinforcements design according to different strut-and-tie models. And the feasibility is verified by the examples. The analysis result shows that the factor of the complementary potential energy deviation is very sensitivity to the rationality of strut-and-tie models. It can be taken as a quantification index of the rationality of strut-and-tie models. The superposition algorithm of strut-and-tie models is derived. Some signification conclusions are obtained.