Abstract: Soil heavy metal-microplastic co-contamination threatens food safety and human health, and bamboo biochar has potential value for soil remediation. However, whether freeze-thaw treatment alters the regulatory performance of bamboo biochar in cadmium (Cd)-microplastic co-contaminated soil remains unclear. In this study, a pot experiment with pepper was conducted using a two-factor completely randomized design. Two biochar types, untreated bamboo biochar (BC) and freeze-thaw-treated bamboo biochar (aBC), were used, and six pollutant treatments were established: no-pollutant control (CK), polyethylene (PE), polylactic acid (PLA), Cd, PE+Cd, and PLA+Cd. The regulatory differences between BC and aBC were then compared. The results showed that freeze-thaw treatment did not significantly change the C, H, and N contents of bamboo biochar, but increased the apparent O/C ratio from 0.188 to 0.200, enhanced C—O-related signals, and increased surface cracks. Compared with BC, aBC did not significantly increase soil pH, but significantly reduced extractable Cd (ExCd) in the Cd, PE+Cd, and PLA+Cd treatments, with reductions of 52.6%-69.7% (P<0.05), and promoted the recovery of catalase and polyphenol oxidase activities. aBC also significantly reduced whole-plant Cd concentration in these Cd-containing treatments, with reductions of 20.0%-25.7% (P<0.05). Pepper growth was more clearly improved in the Cd and PE+Cd treatments, whereas plant growth was most strongly inhibited under PLA+Cd, with plant height reaching only 7-13 cm and fruit yield being zero. Fungal communities were more sensitive than bacterial communities to biochar type and pollution scenario. Overall, freeze-thaw treatment mainly affected soil Cd activity, soil enzyme activities, and plant and microbial responses by changing the surface interfacial properties of bamboo biochar, and its regulatory effects differed between the PE and PLA backgrounds. This study provides theoretical reference and technical support for the remediation of soil Cd-microplastic co-contamination.