The article presents an approach to analyzing the role of interindustry competition in the formation of the sectoral composition of the national economy. The approach is original in its emphasis on competitive mechanisms of interindustry interactions, taking into account redistribution of national economic resources between sectors of the national economy. Three key channels of such interactions are considered: foreign trade, the labor market, and the financial market. Testing the proposed approach on the example of Russia reveals that interindustry competition plays a major role in changes in the sectoral composition of its economy. Considering the channels of interindustry interaction leads to a deeper understanding of processes that cause such changes.