The population in e-retailing ecosystems includes e-retailers,consumers,logistics enterprises,services outsourcing,service outsourcing enterprises of e-retailing,etc.They keep growing through such relationships among them as predator-prey,competition,mutually benefit and parasitism.Base on methodology of system dynamics,this paper constructs causal loop diagram of 4 relationship to study the trends of e-retailing in China during 2001-2030,which includes the scale and spending of online consumes,distribution capabilities and scale of services outsourcing related to e-retailing.The system flowchart,equations and modeling of research process were detailed in this paper.The results show that,the rapid development of China's e-retailing in China is influenced by its own competitive advantage and sustained economic growth.As a parasitic industry,the scale of service outsourcing enterprises depends on the scale of the e-retailing sector and its development level.