The invention provides a positioning system. In one embodiment, the positioning system comprises a Global Navigation Satellite System (GNSS) module, a dead reckoning module, a Geographic Information System (GIS) module, and an calculating module. The GNSS module generates a first positioning data according to satellite communication. The dead reckoning module estimates a second positioning data according to a sensor's measurement data, the first positioning data, and a feedback positioning data of a previous epoch. The GIS module fits the first positioning data to a map to generate a third positioning data taken as a final output of the positioning system. The calculating module integrates the third positioning data and the second positioning data according to predetermined weights to obtain the feedback positioning data of a current epoch, which is recursively fed back to the dead reckoning module for a next estimation.