The game digital industry plays an important role in the development of the digital economy. At present, there are many designs and developments for stand-alone games, but relatively few for multiplayer 3D online games. Combined with the principle of network communication, based on Unity3D, and using MVC architecture, this study designs and implements multiplayer online Action Role-Playing Game (ARPG). For the consistency of online player scenes, Communication protocol, such as position synchronization, weapon synchronization, damage synchronization, etc., has been proposed. Whether the game interface is friendly or not, would greatly affect the user experience of the player, and also affect the overall progress of the game. A general UI framework is designed for it. Due to the network delay, the system is difficult to achieve real-time and accuracy. The player’s position is synchronized, so this study uses the predictive position synchronization method, which effectively reduces the delay error during game running.