E-commerce industry has played a key role in China's economic growth, but studies on the determinants affecting the competitiveness of E-commerce firms are still inadequate. By using a unique survey data of E-commerce firms during 2014-2015 in Guangdong province, this paper exploits the comprehensive effects of platform resource on the competitiveness of those firms. The results find that, the platform resource indeed enhances the competition capability of e-commerce firms, and that the effect is robust among various alternative robust checks. In addition, from the perspective of impact dimensions, platform resource mainly promotes profit ratio and sales' growth ratio. Meanwhile, the promoting effect of platform resource shows remarkable geographic heterogeneity. Further mechanism tests show that, the resource of customer connection and transaction efficiency are the main channels of the support effect of platform resource. The conclusions provide valuable suggestions on how to make platform resource play a key role in increasing the competition capability of those firms.