The security of crude oil supply plays an important role in China's national security, so quantitative assessment for it can provide some policy references for risk prevention. The event data analysis model was employed to quantitatively measure the bilateral relations between China and 21 major crude oil suppliers. The results show that the relations between China and most of its crude oil trading partners are at medium and low levels, but the overall trend has been rising in recent more than ten years, which indicates that crude oil import has a certain risk of political relations but tends to decline. Eleven indexes from five aspects of resources, politics, economy, transportation and military were selected, and the weights of the indexes were determined by combination weighting method. The set pair analysis model was used to evaluate the supply security degree of 21 source countries of China's crude oil import and then the main obstacle factors were identified. The results show that there are significant differences in the supply security degrees of the 21 countries. Some of the Middle East countries, Russia, Venezuela and Kazakhstan have a high degree of supply security, while most African and Asia-Pacific countries have a low degree of supply security. Crude oil resource status, transportation risks and political risks of the suppliers are the main obstacles to the supply security of most suppliers. To prevent risks, China should take policy measures such as pursuing multilateral energy diplomacy and expanding strategic petroleum reserves.