Provided are a method and system for detecting a bot in a Massive Multiplayer Online Role Playing Game (MMORPG) online and in real time. By analyzing a communication pattern between a client and a server, the bot is detected based on parameters such as data length, inter-arrival time and data length auto correlation. Tests using respective parameters are combined to construct a global decision scheme, and thus more accurate detection results can be obtained. An integrated anti-bot defense system can be built by combining other tests such as a Turing test.