In the process of mergers and acquisitions, it's a very important part of success or failure on how to assess the value of target corporate. Thus, it often plays a decisive role in M&A. So it was not only concerned about by the two sides, but also has become a hot theory research problem in M & A. In this paper, aiming at the existing Western M & A theory, we conclude from the two aspects: one is general pricing pricing theory; the other is option pricing theory. In addition, we comment the advantages and disadvantages of various methods in order to present reference for China's M & A decision-making.