Abstract: The effect of initial defect size on the mechanical behavior and failure pattern of CFRP (Carbon Fiber Reinforced Polymer)-confined concrete columns was investigated through theoretical analysis, numerical simulation and experiment validation. Qualitative theoretical analysis was firstly explored to study the effect of initial defect size on the integrity of FRP-confined concrete from macro to micro perspective. Numerical analysis and experimental investigation were then carried out and compared to investigate the failure mechanism of FRP-confined concrete column with initial defects under axial compression force and eccentric compression force. The variation of defect criticality was investigated by varying the layer number of CFRP and cross-section size of concrete columns. The effect of initial defect size on the failure mechanism of CFRP-confined concrete columns was finally demonstrated.