Exorbitant heavy metal embodies certain underlying toxic effects that have been regarded as one of the culprits rendering amphibian populations decline and extinct at a fast clip in recent decades. Cadmium (Cd) is a ubiquitous environmental pollutant that has been concerned as globe issue. The previous study has found that Cd could induce testicular damage, respiratory and nervous system disorders. However,the toxicity mechanism of Cd has not been addressed. Here, we explored the toxicity mechanism study of Cd by investigating the effect of chronic exposure to CdCl₂ on the reproductive system and examine the toxicity mechanism of Cd²⁺ in male Rana nigromaculata. Based on the levels of the Integrated Wastewater Discharge Standard (GB3838-1988) of China and 96h acute toxicity test, six test concentrations, i.e. 0.005, 0.01, 0.05, 0.1, 0.5, 1.0 mg/L, were adopted for the chronic toxicity test by epidermal uptake of CdCl₂ solution. 140 adult male frogs were randomly divided into seven groups, each group embraced twenty. The group treated only with distilled water was set aside as control. All frogs were sacrificed and the testis tissues were collected in the wake of 30 days treatment for the measurement of reactive oxygen species (ROS), protein carbonylation (PCO) and DNA-protein crosslinks (DPCs) levels. The results showed that with the increasing of CdCl₂ concentrations, ROS of test groups became higher than that of control group. In 0.5 mg/L or 1.0 mg/L CdCl₂ groups, ROS increased significantly in comparison with control group (P<0.05). The content of PCO increased notably along with the increasing of Cd²⁺, taken on strong dose-dependent relationship (R²=0.9603, P<0.05). In the presence of 0.5mg/L or 1.0mg/L of Cd²⁺, PCO content was significantly higher than that of control group (P<0.05). Cd²⁺ also induced DPCs levels increasing, which showed obvious dose-dependent relationship (R²=0.909, P<0.05). Compared with control group, we observed significantly difference when the groups treated with 0.5mg/L and 1.0mg/L Cd²⁺. Regression analysis showed that quadratic curve regression were found between PCO content and ROS levels (R²=0.5547), while linear regression occurred between DPCs levels and PCO content (R²=0.8394). Above results indicated that ROS accumulation could induce the PCO content increasing and the PCO might be the upstream signal for Cd-induced DNA damage in the testes of R. nigromaculata. Finally, we proposed that ROS introduced by cadmium played a central role in male reproductive toxicity and ROS may induce the cascade reaction of protein oxidation damage and DNA impairment.