The invention relates to the field of oil-gas exploration and development, especially to a gas detector for logging and a method thereof. The gas detector comprises a laser emission module, a laser sensing module, a signal acquisition and processing module and a display module. By blending multiple functions of laser emission, laser control, second harmonic detection, wavelength modulation and data acquisition and processing, etc., the detector realizes ground real-time online detection of gas components and also can detect multi-component gases simultaneously according to actual situations of mine gases. In addition, the gas detector has advantages of simple operation, high detection accuracy, wide applicability and the like.