With the development of the Internet, people can communicate with each other much more easily. Consumers with similar needs can conduct a collective purchase with potential suppliers by the Internet. Currently, there are many web sites providing collective purchasing for consumers. However, these collective purchasing functions have not fully taken the advantages of the Internet for either consumers or suppliers.Therefore, the first purpose of this research is to explore the possible online collective purchasing models. Based on the number of suppliers and the number of products, six collective purchasing models and related algorithms have been proposed. Further, a comprehensive cybermediary system architecture for collective purchasing was described. Finally, a prototype is built to demonstrate how these collective purchasing models work.