1. A geo-fencing based location detection method, the method comprising: obtaining present geographic coordinates of a terminal, when an update of location of the terminal is detected; and checking whether the obtained geographic coordinates are within a rectangular coverage area denoted by any leaf node in a pre-built tree data structure, and if they are, obtaining an actual coverage area of a polygonal geo-fence within the rectangular coverage area, checking whether the geographic coordinates are in the actual coverage area of the polygonal geo-fence, and outputting a checking result, wherein the polygonal geo-fence is a preset geo-fence, an outer contour of which is a closed polygon, and the tree data structure is a dynamic balanced tree structure which uses a minimum bounding rectangle of the polygonal geo-fence as a leaf node and is pre-built according to predetermined building rules of tree data structure, and wherein the polygonal geo-fence is preset by obtaining geographic coordinates of points clicked by a user for selecting a target area, after a polygonal geo-fence setting mode is enabled, and determining whether a number of the clicked points is not less than three, and if so, setting a polygonal geo-fence, the outer contour of which is the closed polygon, according to the geographic coordinates and a clicking order of the clicked points.