Abstract: A VPN-based method for a mobile communication terminal to access data securely comprises: when a data security device is operating in the mobile communication terminal, the data security device allows the mobile communication terminal to access an intranet but inhibits the mobile communication terminal from accessing an external network; and when the data security device is not operating in the mobile communication terminal, a VPN server inhibits the mobile communication terminal from accessing the intranet. The data security device is disposed in the mobile communication terminal. The data security device cooperates with the VPN server to inhibit the user of the mobile communication terminal from sending protected files to the external network via a network when the data security device is deactivated and to inhibit applications running on the data security device from accessing networks outside the VPN resources to release the protected files to the external network.