Abstract: This paper conducts a research into the bond-slip performance between ribbed steel bars and concrete and derives the displacement solution of a wedge-shaped body with a concentrated force at the tip, and then the relationship between the slip and boundary condition is established based on the wedging action. According to the failure characteristics of a pull-out process, the ascending branch of a bond-slip curve, divided into two stages characterized by whether concrete has been cracked or not, is obtained respectively based on different theoretical models. The slippage is introduced as a boundary condition in the theoretical models, and the variation of boundary conditions is achieved by changing the slippage, so bond stress before the peak value can be obtained at all levels of slippage. The primary factors of descending branch are analyzed; in addition, a negative exponential degrading law is fitted. Finally, the theoretical and the experimental results are compared and analyzed.