Lack of coordination, mutual independence and disorderly competition among China Railway Express platforms gives rise to high logistics costs; in contrast, horizontal collaboration could form a pool of logistics resources with a scale effect to effectively reduce operating costs. This paper presents a methodology to build a coordinated alliance of China Railway Express platforms in a cost-sharing model. A hybrid approach is proposed, using the gravity model of cross-border logistics, variable-weighted Shapley value, cargo volume decision-making model, and cross-border logistics cost analysis model. Seven China Railway Express platforms in southwest China: Chengdu, Chongqing, Guiyang, Kunming, Liuzhou, Nanning and Zunyi, are selected as examples for empirical analysis. The results demonstrate that alliance is an effective way to control costs, however, issues of railway connectivity can lead to deflection of the optimal alliance and insufficient capacity can affect the stability of the alliance.