Polygon simplification in scaleless GIS (geographic information system) is based on the line generalization of polygon arcs, but there may be topological errors in output data resulting from the direct line generalization of polygon's arcs, and the major representation of the error is the intersection of the simplified polygon s arcs. The previous research did not attach importance to this problem. A method of polygon simplification based on Strip-Tree in scaleless GIS is presented in this paper through an all-sided analysis of this problem. Maintaining the correctness of the polygon layer's topoloty, it simplifies the polygon layer according to the output scale. This method has been implemented into an 863 project, and the experimental results show that this method can simplify the polygon layer with high efficiency and can maintain the shape of polygon very well.