The corrosion behavior of Q235B carbon steel is investigated in water, LB medium and oilfield produced water adding Pseudomonas fluorescens FSYZ01. After immersion for 13-days, weight loss of carbon steel with this strain decreased by 32.23%, 54.07%, and 78.34% respectively. XRD results show Pseudomonas fluorescens FSYZ01 inhibited conversion of iron oxides by hindering oxygen from approaching metal surface. FT-IR and XPS results show that specific functional groups and bonds reacted with Fe(II/III) to form a dense and stable chelate-oxide protective layer, thereby inhibiting corrosion. Py-GCMS results demonstrate the bacteria degraded C12 to C20 alkanes in oil. The inhibitory mechanism of crude oil degrading bacteria Pseudomonas fluorescens FSYZ01 on the carbon steel corrosion was proposed, so as to slowing corrosion of oilfield produced water system pipeline and prolonging its service life, helping to comprehend the microbial corrosion in the actual environment.