Foreign investors' merger and acquisition will inevitably produce important effects on competitive actions and competitive patterns of the host countries' markets. This paper demonstrates the mechanism and results of these effects by constructing a Nash-Cournot model, with government as a participator in foreign investors' merger and acquisition. In the model, the factors of asymmetric regulation are discussed in the market competition framework on the basis of foreign investors' merger and acquisition. The basic conclusion is that the asymmetric regulation can affect enterprises' market competition,adjust enterprises' market share and control market structure.