A combined method based on grey relational analysis and entropy method was used to proposed a evaluation model for Mergers and Acquisitions (M&A) effectiveness, in which the entropy method was introduced to determine the weight of each indicator, and the grey relational analysis method was introduced to evaluate and rank the M&A effectiveness for each object. Then we used the evaluation model to evaluate the M&A effectiveness of six combined firms, and the results showed that this model is practical and useful.