In this study, the electrochemical corrosion behavior of iron-oxidizing bacteria Thiobacillus ferrooxidans on Q235 steel was investigated. The results showed that the bacteria obtained electrons from Fe²⁺ and transferred them to oxygen used as an electron acceptor when Fe²⁺ was oxidized to Fe³⁺. Simultaneously, it was found that the dissolution of samples in the T. ferrooxidans group was accelerated by a weight loss test, surface morphology observation and electrochemical measurements. That meant the metal coupon was corroded faster. The corrosion products were found to be jarosite by XRD and FTIR. The corresponding corrosion mechanism of T. ferrooxidans was explained from the perspective of chemical thermodynamics and electron transfer. In addition to the anodic dissolution of Fe, it was proposed that the comproportionation reaction was also one of the causes of accelerated corrosion of carbon steel in this study.