In this study, the dissipation and transformation of acetamiprid were investigated during the cowpea pickling process and the toxicity assessment software Ecological Structure Activity Relationship (ECOSAR) and the Toxicity Estimation Software Tool (T.E.S.T.) were used to predict the toxicity of acetamiprid and its transformation products (TPs). The results showed that acetamiprid was rapidly degraded during the pickling process with a degradation rate constant of 0.96761 and a half-life of (34.95 ± 0.78) d. Four TPs from acetamiprid were found during cowpea pickling process. Among them, the oral lethal doses of TP1 and TP2 in rats were 358.17 and 385.7 mg/kg, respectively, which belonged to the “hazardous” category, and the developmental toxicity of TP1 and TP2 was significantly increased compared with that of acetamiprid. In addition, acetamiprid, TP1, TP2, and TP3 were detected in all real samples. The highest mass concentration of acetamiprid was 473.8 μg/L and the median concentration was 41.1 μg/L. These results reveal the degradation and biotransformation of acetamidine during pickling of cowpea and contribute to a better understanding of the possible health risks of pickling foods.