Abstract: The species and quantities of hazardous chemicals are increasing year by year with the rapid development of national economy in coastal area of China, and the leakage risk of hazardous chemicals is increasing, which pose the potential threat to marine ecological environment.This article focused on the Rizhao Lanshan port, which is the largest bulk hazardous chemicals distribution center, and took the paraxylene that the annual throughput account for approximate 41% of total amount of hazardous chemicals as the research object, then forecasted the marine environmental impact of the accident that paraxylene leaked into sea with the maximum credible quantity in three scenarios.The simulation prediction results showed that the high concentration range of paraxylene was mainly located in the port and near the port area when leakage accidents happened on shore (50 ton paraxylene leakage of operational accident in chemical terminal or 800 ton paraxylene leakage of chemical tank accident), and there was no impact on the three ecological protection zone.When 2, 000 ton paraxylene leakage happened on the channel due to transport ship accident, the leaked paraxylene under the SSE and in the ebb phase would begin to affect the three ecological protection zone located in northeast 4 hours later, and the maximum concentration was 5 mg/L, while all the leaked paraxylene would volatilize 8 hours later, so the impact duration time is very short.However, all the leaked paraxylene under other conditions would evaporate before affecting the three ecological protection zone.