Abstract: The distribution of confining stresses and bending moments along 4 side-plates in concrete filled tube as a compression member are introduced. The plastic hinge lines formed in side-plates in the ultimate states are assumed and the average confining pressure is computed. By requiring the same confining pressure is achieved in concrete filled circular pipe in its ultimate state, the corresponding radius-thickness ratio of the pipe is determined and equivalent confining coefficient is obtained. The equivalent coefficient is presented and compared to the test result, and is found to be able to predict the average strength of the test results. Finally when the full strength weld between side-plates is required is provided.