A parking spot detection system is provided with a detection unit, a map database and a processing unit. The detection unit acquires position data and intensity data of a plurality of data points in an environment space. The map database provides map information. The processing unit is coupled to the detection unit and the map database and determines whether a geometric shape formed by adjacent data points is of a parking space according to the intensity data of the data points; and if the geometric shape is determined to be of the parking space, the processing unit further integrates the geometric shape and the position of the parking space into the map data according to the position data of the data points.