The present invention relates to a GPS/dead-reckoning combination system and an operation method of the same. The GPS/dead-reckoning combination system includes a GPS receiver that receives an absolute position data of a moving unit from a GPS; an inertia sensor that measures a displacement of the moving unit based on a dead-reckoning method; a forward and backward movement judging unit that judges a state data concerning a forward or backward movement of the moving unit; a dead-reckoning processor that measures a running distance and a position of the moving unit based on a dead-reckoning method in reference with the data provided from the inertia sensor and the forward and backward movement judging unit; and a computation unit that estimates the current position of the moving unit in reference with the data from the GPS receiver and the dead-reckoning processor.