Objective To systematically evaluate risk prediction models for 30-day unplanned readmission in patients undergoing coronary artery bypass grafting (CABG). Methods We searched PubMed, EMbase, Cochrane Library, Web of Science, CINAHL, CNKI, CBM, WanFang, and VIP databases from inception to June 25, 2025. Two investigators independently screened literature, extracted data, and assessed bias risk/applicability using PROBAST criteria. Results Thirteen studies comprising 17 prediction models were included. Ten models reported the area under the receiver operating characteristic curve (AUC) for modeling (0.597-0.906), ten models reported the AUC for internal validation (0.57-0.92), and twelve models reported the AUC for external validation (0.537-0.865). Core predictors included age, female sex, diabetes, and heart failure. All studies had a high risk of bias. Conclusion The research on risk prediction models for 30-day unplanned readmission in patients undergoing CABG is still in its exploratory stages. Some models exhibit insufficient performance, and there is a need to enhance the processes of model validation and performance evaluation. It is expected that future efforts will focus on developing prediction models with excellent performance and high applicability, to assist healthcare providers in the early identification of high-risk patients for readmission.