Asymmetric information makes the allocation of resources always not the optima between investment institutions and small and medium-sized enterprises (SMEs) in the traditional financial environment, resulting in the problem of expensive financing for SMEs and the investment institutions gradually narrowing their profit margins. Under the background of Social Networks, by introducing e-commerce platforms in the traditional model of investment institutions directly providing financing for SMEs. Therefore, we consider the direct participation mode of the e-commerce platform as a fund supplier and the indirect participation mode as an information supplier. Furthermore, we analyze the impact of the key parameters on the financing cost of SMEs by optimal loan quantity in the market and expected utility of participants use of numerical cases. We find that the indirect participation model of e-commerce platform result in lower the borrowing threshold and cost, whereas the credit line is higher under social networks environment. Further evidence shows that the behavior of investment institutions and SMEs to maximize the expected utility will prompt the e-commerce platform to transform from a direct participation model to an indirect participation model, thereby reducing the risk of loan default in the entire market.