Under digital convergence, the market structure has changed which cause the traditional market definition is no longer applicable. Many industries and firms have take action of cross-industry M&A and integration. In contrast, regulations and ¡§new¡¨ market definition has not appeared which cause antitrust authorities deal with the case of the M&A under digital convergence has no quantitative tools. Our study has found that the market structure under digital convergence almost is two-sided market and multi-sided market, so we use the modified Critical Loss Analysis which Evans and Noel (2008) proposed to be the market definition tool under digital convergence. Subsequently, we use the merger case of TFN media and Kbro to do empirical analysis. By the empirical results, we find out that the relevant market of cable TV has to expand. The IPTV and online play will be the competitive product that the market structure of cable TV will be changed radically. Under digital convergence, market definition may not precisely than traditional, but it still could provide antitrust authorities an effective quantitative evidence, and with the economic theory of qualitative analysis which could make policy analysis more integrity.