In this paper, post-tensioned connection between concrete and cast iron plate having shear-key was adopted. Frictional resistance acts when there is no displacement between concrete and cast iron plate, shear-key also act to transmit stress to RC beam at the same time as the frictional resistance when the displacement occurs. Each specimen consists of RC beam and plate simulating post-tensioned connection. Ten specimens were tested. The parameter are type of plate, with or without the shear-key, the height of the shear-key, amount of the shear-key, difference between the post-tensioned force and whether or not applying vertical tensile force. In conclusion, it was needless to think their displacement by post-tensioned connection. And the strength of specimens with shear-key is presented by the sum of friction resistance and bearing resistance by using anamnestic formula.