Abstract: The high-temperature pyrolysis oxidation method was adopted to prepare reed biochar, and reed biochar was used as the immobilized material to load the dominant petroleum hydrocarbon degrading bacteria, and the effects of biochar immobilized microorganisms on the remediation effect and enzyme activity of petroleum hydrocarbon contaminated soil were studied. The results showed that after 40 days of remediation of petroleum hydrocarbon contaminated soil by immobilized microorganisms with reed biochar, the removal rate of petroleum hydrocarbon in soil reached 55.01%, which was significantly higher than that of single biochar (45.82%) and blank treatment group (24.83%). It was also found that biochar immobilized microorganisms could significantly improve the activities of dehydrogenase, catalase, urease and polyphenol oxidase in soil. The use of biochar immobilized microorganism technology can not only improve the remediation efficiency of petroleum hydrocarbon contaminated soil, but can also significantly increase the soil biological enzyme activity.