In order that the GPS could be used adroitly and the investigate precisions could be improved in forest resource inventory,based on the introduction of the basal knowledge of geography coordinate,this paper has represented the method transform parameter one another between the mother earth coordinate and the plane coordinate;expatiated the applied instance of the GPS in forest resource inventory;analyzed the precisions of orientation,navigation and quadrature with GPS,as well as some noticed proceedings for heightening the precisions,by exemplifying GARMIN GPS ETREX.The conclusion has been brought forward that in the same projection zone,the transform parameter of the mother earth coordinate and the plane coordinate determined with more than three triangle control water points,can satisfy the precisions of orientation and navigation, can satisfy the quadrature precision on condition that the investigated area is more than 3 hm~2,in forest resource inventory,with GARMIN GPS ETREX;the bigger the area is,the higher the precision is.