A Global Positioning System (GPS) system comprises a tracking device, a base station, and a mobile station. The tracking device has a GPS receiver for receiving GPS signals from a plurality of GPS satellites and generating position information. The base station complies with Global System of Mobile communication (GSM) standard and communicates with the tracking device by means of a Short Message Service (SMS) signal. The mobile station receives the position information via the base station for showing the position of the tracking device.