Abstract: Structural model tests of back tube were performed to optimize the design of back tube of powerhouse of the Three Gorges Project. On the basis of model material tests, steel fiber concrete, conventional concrete and lack bar concrete tests were respectively conducted. Studying key points were initial loads, limit loads, concrete strains, and stresses of reinforcement bar and steel lining. The characteristics of back tube structures made of fiber concrete and conventional concrete are compared. Interaction between fiber concrete and reinforcement bar are analyzed. The results of test indicate that under samecondition employing steel fiber concrete can obviously increase capacity of resistance crack, but capacity of limiting crack of concrete structure still mainly depends on reinforcement bar. Coalescence of both steal fiber and bar in concrete can obtain better structure performances.