The corrosion process and difference between base metal and weld were explored by simulating immersion corrosion test of L245 pipeline steel with welding seam under the action of sulfate-reducing bacteria. Immersion corrosion test in SRB environment were performed at different periods. SEM&EDS, FIB-SEM, CLSM and other analysis methods were used to study the corrosion behavior of weld zone and base metal zone in SRB environment. The results showed that Localized corrosion happened under the biofilm, submembrane pitting were becoming more aggravated with the immersion time extending. The biofilm on weld zone generated faster than that generated on base metal zone in the early stage 24 h, the surface was completely covered by biofilm until 72 h immersion. At the end stage 168 h, biofilm structure showed that a mass of SRB existed in the biofilm, which was the main factor of the pitting corrosion. By measuring the pitting, it was found that the average and the maximum pitting depth on weld zone were higher than that on the base metal zone, and pitting corrosion was more severe in the area near the fusion line. The growth of biofilm accelerated the corrosion of carbon steel L245. The weld zone was more sensitive to SRB-induced corrosion. This study revealed the corresponding relationships among bacterial growth trend, biofilm growth process and pitting development. The composition, metallographic structure deference between weld and base metal zone and electrical activity of SRB were the main factors that caused more serious pitting corrosion on weld zone compared to the base metal zone.