As competition in the cross-border logistics-service market intensifies and demand rises, enterprises with third-party logistics (3PL) combine logistical and financial services to provide comprehensive services. This study considers a secondary supply chain consisting of a cross-border e-commerce enterprise and a 3PL enterprise. When cross-border e-commerce enterprises lack funds, 3PL enterprises can provide them with inventory pledge loans. Thus, we establish a Stackelberg game model between the abovementioned parties. We consider the stochastic fluctuation of exchange rate and demand, establish a combined decision model of the logistics-service level and financial service pledge rate of the 3PL enterprise when logistics services affect offshore market demand, and prove the existence of an optimal solution. Studies have shown that the optimal logistics-service level and pledge rate increase with an increase in import tariffs and logistics sensitivity coefficients in offshore markets. Meanwhile, they decrease with an increase in the capability coefficient of 3PL enterprises, exchange rate fluctuation, default rate, and price sensitivity factor in offshore markets. In addition, the more capable 3PL enterprises are, the greater the expected profitability of the entire supply chain. We also utilize authentic data to verify the abovementioned inference and establish its validity.