Based on the technique of Geographic Information System and mathematical models, Dongguan Agricultural Modernization Experimental Field for Red Soil Areas was taken as the research site for soil quality evaluation.ArcInfo was adopted to data processing, and overlay analysis to spatial data analysis.Evaluation units were determined by combination of evaluation factors.AHP was applied to judge the weight of each evaluation factor.After evaluation criteria was fuzzified, variable weight evaluation was carried out.The results were calculated and mapped by using ArcView GIS software.Dif ference between results from evaluation with variable and constant weight was compared and analyzed.Results show that soil quality evaluation with variable weight is better than with constant weight.