In E-Commerce, consumers and service suppliers can find the services through the searching of Mobile Agents (MA).The suppliers disassemble the service requests of consumers into the sub-requests. Then suppliers respond the subrequests cooperatively. Thus the Service Supply Chain(SSC) can be formed. But the existing bottom-up and upbottom supply chain formation fashions cannot be adapted to the SSC in distributed environment of E-Commerce. Task Dependency Network is exploited to illustrate the service relationship among consumers and suppliers. The formation of SSC with some simulations is elaborated. Then the influence on the formation of SSC caused by the type of service suppliers, the quantities of MA and its variety in number is elucidated.