Abstract: In this study vibration analysis of multi-cracked beam under moving mass was investigated. Timoshenko beam model was considered and governing equations were found. Assumed-modes method was applied to find eigenvalues and eigenvectors of cracked beam. Cracks in the beam structure were modeled as local flexibility and were replaced by transverse and rotational spring pair. The compliance factors of springs were found based on fracture mechanic theorem. Due to cracks, beam was divided into segments. Compatibility equations were implemented to relate every two segments. Different boundary conditions were considered and deflections were found and debated. Natural frequencies were calculated and compared. It was observed that, crack attenuates beam structure and reduces natural frequency effectively. Mid-span of the beam was found as the critical point for crack location. Mid-span deflection for various mass speeds was calculated and the critical speed was defined. Results were verified against those which were found through Discrete Element Technique (DET) and Finite Element Method (FEM).