Ecological factor field is presented to quantify spatial heterogeneity of physicochemical factors in bound inland waters. On August 21-23, 2001, a water sampling was carried out in the Baoan Lake at eighty-one stations with assistant of a GPS setting. The results of laboratory analysis were put into computer to establish the GIS database of physicochemical factors of the Baoan Lake. Under the support of GIS software ArcView 3.2, ecological factor fields were simulated using Kringing interpolation technique. Then Grid statistics of simulated fields could demonstrate general characteristic of each environmental factor in the lake. The figures of fifteen simulated ecological factor fields reflected distinctly spatial concentration distributions of these factors. Also, factor concentration in any position could be easily read from the figures. Field fluctuation well described strong heterogeneity of the water environment in the lake. Variation tendency differs to each other among all ecological factor fields. The pattern of heterogeneity, while can't be explained by only one reason, is introduced by the integrated effect of natural process and artificial disturbance. It suggested that lake uses by human being play more important role in the heterogeneity formation. Continuous effluents of domestic wastewater could be considered as another key element to disturb the homogeneity of water phase. Physicochemical characteristics calculated by grid statistics method brought an overview on water quality of Baoan Lake. The concentration of TN and TP was 0.731 mg . L-1 and 0.123 mg . L-1 respectively, implying a high trophic status in Baoan Lake.