Carbendazim, a widely used benzimidazole fungicide, poses significant environmental and health risks, necessitating sensitive analytical methods for its determination in food and environmental samples. A novel dual-emission iron and nitrogen co-doped carbon dots nanozyme with fluorescent bands at 440 nm and 522 nm was developed, functioning simultaneously as both ratiometric probe and peroxidase mimic. The nanozyme catalyzes 3,3’,5,5’-tetramethylbenzidine oxidation in hydrogen peroxide presence, generating blue oxidized 3,3’,5,5’-tetramethylbenzidine that quenches the 522 nm emission while 440 nm serves as internal reference. Carbendazim scavenges reactive oxygen species, suppressing oxidized 3,3’,5,5’-tetramethylbenzidine formation and restoring 522 nm fluorescence, producing a self-calibrating fluorescence ratio immune to environmental variations. Additionally, the reduction of oxidized 3,3’,5,5’-tetramethylbenzidine color upon carbendazim addition enables colorimetric detection. Kinetic studies revealed excellent peroxidase-like activity with Michaelis-Menten parameters. The dual-mode sensing platform achieved linear responses of 3.0–18.0 ng/mL (colorimetric, limit of detection = 1.25 ng/mL) and 1.0–38.0 ng/mL (fluorometric, limit of detection = 0.64 ng/mL) for carbendazim detection. Successful application to fruit and water samples demonstrated excellent accuracy with recovery rates of 96.89–102.00%, representing the first integration of carbon dots-based peroxidase mimicry with ratiometric fluorescence detection for carbendazim analysis.