Based on investigation data on petroleum hydrocarbon (PHC) in April, August and November 1981 in bottom waters in Jiaozhou Bay, we analyzed the content and distribution of PHC. Results showed that PHC contents in April, August and November 1981 in bottom waters were 0.028-0.123 mg L -1 and were meeting Grade II (0.05 mg L -1 ) and III (0.30 mg L -1 ) in National Sea Water Quality Standard (GB 3097-1997). PHC contents were decreasing from the inside of the bay mouth to the outside of the bay mouth in April and August, yet were reverse in November. We found the migration rules of PHC in bottom waters in marine bay, that were the substances could be generated from both the bay and the open waters by means of vertical water's effect, and the PHC contents were diffusing from the bay mouth no matter from the bay of the open waters.