A method and a system for simultaneously supporting network sharing and data synchronization are provided for a first operating system (OS) and a second OS, wherein the first OS is connected to a network. The present method establishes a virtual network between the first OS and the second OS. Then, the second OS is connected to the first OS through the virtual network, so as to connect to the network through the first OS. The virtual network can also be used for synchronizing data of the first and second OS. As a result, the convenience of using different OS at the same time can be improved.