Carbon fiber reinforced polymer/steel (CFRP/steel) bonded joints are widely used in the reinforcement of bridge and ship structures, and their mechanical performance is significantly affected by overlap length. To address the insufficient understanding of damage evolution mechanisms and the limited recognition accuracy in existing studies, a damage monitoring and overlap length identification method is proposed by integrating acoustic emission (AE) and digital image correlation (DIC) techniques. Four overlap lengths of 25, 50, 75, and 100 mm are tested under quasi-static tensile loading. During the tests, AE signal features including amplitude, energy, centroid frequency, root mean square (RMS), and duration are collected, while full-field strain distributions are obtained using DIC to analyze the damage initiation, propagation, and failure mode evolution of the joint. The results show that the damage process can be divided into three stages, with five main failure modes identified: steel deformation, fiber fracture, matrix cracking, adhesive failure, and cohesive failure. In addition, overlap length has a significant influence on the mechanical performance of the joints, and the joint with an overlap length of 100 mm achieved an ultimate tensile load of 60.70 kN, approximately twice that of the 75 mm joint. Based on the AE features, an extreme gradient boosting (XGBoost) classification model is formulated for identifying the overlap length of CFRP/steel bonded joints, achieving a recognition accuracy of 94%. Furthermore, the shapley additive explanation (SHAP) method is incorporated into the model to quantify the contribution of each feature, revealing centroid frequency, RMS, and duration as the most critical parameters. This study reveals the influence of overlap length on damage behavior of the joint, effectively uncovers the relationship between AE features and damage states, and improves the accuracy and interpretability of damage prediction, providing valuable guidance for failure mode prediction and structural optimization design of CFRP/steel bonded joints.