Small and medium-sized enterprises generally have high default risk due to the characteristics of low concentration, long chain and large seasonal fluctuations. The implement of supply chain finance and factoring mainly relies on core enterprises in supply chain. However, the development of platform economy has transformed the supply chain structure from independence to coupled based on the core enterprise, namely degree of centralization. Therefore, with respect to a two-echelon supply chain which comprised of a capital-constrained supplier and a core retailer, this paper analyzed the effect of degree of centralization and guarantee to the factoring financing in the context of financing default risk based on the Stackelberg game and numerical simulations. Three guarantee scenarios are considered: no guarantee, third-party partial credit guarantee when guarantee fee is borne by the supplier, or retailer. The outcomes reveal that guarantee can efficiently reduce the supplier’s financing interest rate and financing costs, but a higher degree of centralization is not always beneficial to financing efficiency and supply chain operations. In addition, it is worth noting that the retailer’s profit and profit ratio is decrease with the degree of centralization, even the increase in degree of centralization means that the operating structure is more centralized. Furthermore, the absolute profit of the supplier is higher and the relative profit is lower when retailer bears the guarantee fee. With the jointly consideration of degree of centralization and guarantee coefficient, our analysis shows that the optimal default risk management mechanism is retailer bears the guarantee fee when there is partial credit guarantee from third-party