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. A pot experiment with green 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-pollution control (CK), polyethylene (PE), polylactic acid (PLA), Cd, PE+Cd, and PLA+Cd, to compare the regulatory differences between BC and aBC. 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 led to more surface cracks. Compared with BC, aBC did not significantly increase soil pH, but significantly reduced extractable Cd (ExCd) under 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 under these Cd-containing treatments, with reductions of 20.0%-25.7% (P<0.05). Green pepper growth was markedly improved under the Cd and PE+Cd treatments, whereas plant growth was most strongly inhibited under the PLA+Cd treatment, with plant height reaching only 7-13 cm and fruit yield zero. Fungal communities were more sensitive than bacterial communities to biochar type and pollution scenario. Overall, freeze-thaw treatment mainly affected soil Cd activity, enzyme activities, and plant and microbial responses by changing the interfacial properties of bamboo biochar, and its regulatory effects differed between the PE and PLA backgrounds. This study provides theoretical and technical guidance for the remediation of soil Cd-microplastic co-contamination.