In recent years, with the deepening application of information technology, e-commerce became a more important role in the world economic system and gradually became the new economic growth of many countries. At present, there are many different kinds of models of e-commerce, and the corresponding transaction system structures are also varied. In addition to the producers and consumers, the third-party transaction platforms, logistics service providers, payment middlemen are also important in these e-commerce models. They provide commodity circulation services to realize the trade of commodities, and we call them middlemen. Different kinds of middlemen constitute the e-commerce transaction systems (Figure 1). Middlemen could be divided into two types. The first type of middlemen does not have the ownership of commodities. They provide transaction services and earn a profit by selling the services to others, such as e-commerce platforms providing information services, logistics companies providing logistics services, banks and other payment companies providing payment services and so on. The second type of middlemen have the ownership of commodities and earn a profit by selling the commodities to others. They organize the transaction themselves and use the information services, logistics services and payment services provided by the first type of middlemen to finish the transaction. Chandler (1978) called the former commission middlemen and the latter markup middlemen. This makes us curious about the evolution of the division of labor in e-commerce transaction system. How many types of middlemen would exist in the future? What services would they provide? We study the decisions of middlemen about the division of labor in ecommerce transaction system to solve these problems in this paper. The study on the division of labor started in eighteenth century. Smith (2015) put forward the origin of the division of labor in an Inquiry into the Nature and Causes of the Wealth of Nations. He believed that different producers have different production efficiencies to produce different products, which forms the absolute advantages of producers. Producers would produce the products in which they have an absolute advantage, thus the division of labor appears. Ricardo (1913) proposed the theory of comparative advantage. He thought absolute advantage is not the necessary condition for trade.