Since the advent of the Duverger proposition，there have been numerous discussions on the interaction between the electoral system and the party system，and the academic community has now largely reached a consensus on the majority decision system. The Mixed Electoral System，an emerging electoral system after the Second World War，has emerged and evolved over the past seven decades. Among the 185 countries in the world that currently have relatively complete and independent electoral systems，32 have adopted Mixed Electoral System. Since the reform of the electoral system in 1994，Japan has so far completed nine general elections for the House of Representatives under the Mixed Electoral System and has gradually grown to become a typical country of this system. The article chooses Japan as the only study of the Mixed Electoral System country in the hope that it can fully discuss the ability of the Mixed Electoral System to influence the party system，not only in terms of intensity but also in terms of direction，based on a quantitative analysis. This paper will use quantitative research methods of correlation and regression analysis to evaluate the level of influence of the mixed electoral system on the Japanese political party system through a cross-sectional and longitudinal comparison. Using a hypothetical-deductive approach，the “effective party discount rate” and the “deviation contribution rate” of political parties are calculated for different types of constituencies，seat allocation methods and the Mixed Electoral System of linkage to determine the direction of this influence. Having obtained the relevant conclusions，this article also judges the future prospects of the two parties’ coalition based on the perspective of electoral politics by examining in detail the established cooperation achievements of the LDP-CGP Alliance.