The NS-3 based emulation system is designed for developing and debugging new UWN protocols or application software, as well as conducting large-scale simulation experiments. It uses the Underwater Acoustic Network (UAN) module of NS-3 to simulate the physical layer devices and underwater acoustic channel. Virtual machines are employed to emulate the UWN application and protocol stack programs. Programs running on virtual machines are connected to nodes simulated in NS-3 via TAP bridges and TAP devices.