The invention discloses a system and a method for tracking a weaving arc space weld based on an MEMS (micro-electromechanical systems) sensor. The system comprises a manipulator, a welding power source, a wire delivery machine, an electric arc sensor, a built-in type MEMS sensor welding gun, a weaving arc space weld tracking signal processor, a welding gun tilting angle operator, a swinging direction operator, a welding gun attitude real-time adjuster, and a welding expert system. The system adopts a core principle that the space weld can be tracked by the weaving arc space weld tracking method based on the MEMS sensor, and has the advantage that the space attitude of the welding gun is collected by an arc sensor, a gyroscope and an accelerometer, and the tilting angle and swinging direction of the welding gun are automatically adjusted by weld angle differential identification, vertical displacement orientation and other methods, so that the real-time tracking of the space complicated weld is realized.