This paper first briefly introduces the functional advantages and development status of WeChat applets, and discusses in detail the design methods and key technologies used in developing WeChat applets. This system is a group sports activity system developed by WeChat applet. It adopts C/S software architecture and MVC development mode. The development of front-end client mainly uses the development framework of WeChat applet, and uses JS to generate dynamic content on the page. Development tools use WeChat applet-specific development tools. Server-side development is written in the Java language, using the SSM framework, the Tomcat server as well as the MySQL database. The data format for interaction between the front and back ends is in JSON format.