Abstract: Geochemical survey is an important method of mineral potential evaluation, especially important to prefercial selection in mineral prospective area. But in practice if using the same anomaly threshold to outline all anomaly, locations of mineral occurence are usually different from boundary of anomaly. Based on comparative analysis, we found that it's an effective way using window moving average data to draw geochemical isoline map and corresponding anomaly map. In northwestern China(including five provinces), the applicable length of moving average window is 49km×49km. The problem of anomaly dislocated can be solved by this way. High background values are obviously weakened and low background values are heightened in this way. At the same time, the distribution of regional anomaly belt is illustrated well and the spatial features of regional structure and ore-controlling structure are reflected indirectly.