Abstract: Based on the potential risk of Petroleum enterprises′ crossborder merger and acquisition project in China，this paper discusses the principle of fuzzy mathematics applied in the assessment method and analyzes the structure system of evaluation model，the index weighting，risk rank，and the evaluation to risk grades.The result indicates that petroleum enterprise should particularly strengthen the capacity to deal with unexpected political events，and be fully aware of host country′s laws in order to reduce legal risks，hence develop greater capacity in making strategic decisions.This is of great significance in China′s energy security.

Key words: petroleum enterprise in China, cross border merger and acquisition, risk, fuzzy AHP, risk prevention measures