Abstract: We improve traditional difference expansion algorithm by modifying the formulas in the embedding and data extracting procedure,it need not calculate the mean coordinate values of the vertex pairs,only need embed the coordinate value of the first point along with the payload.The experimental results show that the algorithm can recover the original maps from the watermarked ones and attract the embed watermark,and it is capable of hiding more secret at low map distortion and the data error is more controllable,and the data has better confidentiality.