At the end of the 13th Five-Year Plan period, based on the current and future environmental changes at home and abroad, the Central government proposed to establish a new development pattern with domestic major circulation as the main body and domestic and international dual circulation promoting each other, which asks for higher requirements on the level and quality of opening-up. Based on Chinese firms'' data from the World Bank''s 2012 survey, whether digital transformation promotes firms'' outer circulation and the possible influence mechanism and implementation path are discussed. The mechanism analysis shows that digital transformation strengthens firms'' data capital, and the data capital becomes a strategic asset and innovation enabler, reduces the transaction cost, and thus promotes firms'' outer circulation, especially promotes firms to directly participate in the outer circulation. Empirical studies find that digital transformation has significantly promoted firms'' outer circulation, especially promoted firms to directly participate in the outer circulation. The heterogeneity analysis shows that compared with small and micro firms, digital transformation has a more significant effect on the outer circulation of large and medium-sized firms. Compared with firms which not located in main business cities, digital transformation plays a more significant role in promoting firms which located in main business cities to directly participate in the outer circulation. Compared with firms which located in main business cities, digital transformation plays a more significant role in promoting firms which not located in main business cities to indirectly participate in the outer circulation.