To deal with the high cost and the inflexible opening hours for traditional labs, a 3D virtual laboratory system based on X3DOM engine has been designed. The system is developed based on the browser/server architecture. The server provides laboratory scene, virtual experimental instruments, XML template, and file storage and access services. The browser uses MVC design pattern. According to the idea of component development, X3DOM is used to render the view. Javascript is used to build the simulation module and the extensible component library is built. Taking the Ping experiment in the computer network course as an example, the design and implementation of the virtual laboratory has been verified. The results show that the system can be used to effectively assist experimental teaching.