The invention belongs to the field of air quality detection, and particularly relates to an air purifier, a laser dust concentration sensor and a detection method thereof. According to the laser dust concentration sensor, a correcting photosensitive part used for correction is additionally arranged at a specific position in a light trap, after incoming laser is absorbed and reflected by the interior of the light trap, intensity of light irradiated on the correcting photosensitive part is substantially weakened, and voltage output converted from output current of the correcting photosensitive part through a special pulse voltage output circuit is read as a correcting voltage. The sensor corrects a real-time pulse voltage output from a detection photosensitive part according to the correcting voltage, and dust concentration is determined with the corrected pulse voltage as a basis. The laser dust sensor has high accuracy under different temperatures through low cost and a simple technology. In the same way, the air purifier internally provided with the laser dust concentration sensor can achieve the air purification purpose better, and user experience is improved.