Platforms of cross-border e-commerce make it come true that the small and medium-sized enterprises can take part in foreign trade. Meanwhile, they have changed the traditional party patterns subject to the customs and made it ambiguous concerning the liabilities among those parties. Nowadays it is common that platforms bear the independent liabilities or supplementary liabilities in many countries. The Customs Announcement No. 26 in 2016 is one of the most comprehensive provisions on the platform of cross-border e-commerce in China until now. But there are still some obligations of platform inexplicit and lacking of upper law basis. Those duties may be legalized by regulation revising and theory reference.