With the rapid development of economy, it has been more and more difficult for enterprise relying on its internal expansion to grow up. As Mergers and Acquisitions become one of the effective means of expanding, M&A risk always exists. To scientific analysis and rational control of M&A risk through the whole stage, is the key factor that decided the success or failure of M&A. Though lack of M&A risk analysis results in a lot of M&A failure cases, it still has not caused enough attention of us. Therefore, we must know how to identify, analysis, and control and mitigate M&A risks with appropriate risk prevention measures. In order to ensure the M&A activities carried out smoothly, promote the enterprise’s size and strength. In this paper, the characteristics, causes and recognition of M&A risk are briefly described. And we tried to find methods of M&A risks defensive In accordance with the analysis of different phases of M&A.