Limited by the free cash flow, small and medium enterprises (SMEs) need external financing to achieve positive operating, therefore the core business credit guarantee loan is an effective means. A guarantee loan model under the down- risk-averse bank is constructed. The order quantity and wholesale price parameters decisions are used to evaluate the supply chain risk-free capital transfer process. By considering the guarantee fee rate and risk guarantee ratio design, as well as bank interest rate portfolio model, the optimal decision of the loan guarantee system is determined. The results show that: the funds constrained supply chain with loan availability has a combination of the optimal order quantity and the wholesale price, and vendor sales exist most value; there is an optimal risk sharing ratio during the guarantee loan process, and by designing the rational risk control model, SMEs can get funds, reaching the collaboration of the supply chain.