A method for estimating the rebar force crossing a crack under model I loading in RC beams using the crack mouth opening displacement (CMOD) is proposed based on fracture mechanics accounting for bond slip at rebar-concrete interface. In the method, a CMOD is regarded as a consequence of the combined action of applied loads, rebar bridging forces and the bond slip. The CMOD due to these three contributors are estimated through an integral transformation based on fracture mechanics and a bond slip model. Since the CMOD due to bond slip is included, the tension stiffness effect is considered implicitly. Theoretically, the rebar force is estimated through the proposed method and the inverse analysis of COD profile using the same noisy synthetic COD profile. The smaller error of the proposed method in most cases demonstrates its reliability. The proposed method is further investigated through estimating the rebar force of an RC beam subjected to four-point bending load in laboratory, where acceptable accuracy is achieved. Conclusively, as the proposed method is dedicated to rebar force estimation of an RC member using CMOD, it provides a potential NDT&E approach for existing structures where the COD profile cannot be measured.