中文摘要：

原TOPMODEL结构中流域平均地下水深计算缺乏物理意义，缺水深系统偏小，带来水量平衡的误差。本文对TOPMODEL中平均地下水深计算展开分析，讨论原TOPMODEL中平均地下水深计算产生负值的现象和原因，并通过引入临界地形指数和非饱和面积地形指数均值的概念．采用新的平均地下水深计算方法应用于TOPMODEL中。分析了新的平均地下水深计算方法的解析解，并通过算例分析该方法与原方法的区别。将新的平均地下水深计算方法结合到TOPMODEL中，结果计算流域平均地下水深不再出现负值，更具物理意义，壤中流计算也更合理。

英文摘要：

The algorithm of mean groundwater table is lack of physical significance in the original TOPMODEL, which leads to a systematic underestimation of the catchment water storage deficit and bias in the water budget accounting. Here, the algorithm of mean water table in TOPMODEL was analyzed to discuss the reason of negative value phenomena in mean water table, and deduce the improved algorithm for it by introducing the concepts of critical topographic index and mean value of topographic index in unsaturated area. Educe the analytic solutions of the improved method, and express the difference between improved and original methods through figure example. Combine the improved algorithm of mean water table to the original TOPMODEL, and the results show that the value of the simulated mean water table would not be negative, which more follow the physical significance and the calculation of subsurface flow is more reasonable.