Historical data about withdrawal of regional groundwater serves as a foundation for better evaluating and scientifically managing the groundwater resource. However, due to limitations of management system and workload etc., statistical data shows that groundwater exploitation is much less than what we expect in fact. In this study, we take the plain area of Tianjin as an example, the historical dataset on groundwater withdrawal is estimated reversely based on the coupled numerical model-groundwater flow and land subsidence via Modflow2005. Specifically, pumping rate serving as an input in the model is continuously modified until the numerical head distribution simulates observed value at every county in a specific period. Nonetheless, the pumping rate is also constrained by the value estimated by statistical method and quota method. Finally, the mean annual value of groundwater exploitation during 1998 to 2008 is estimated to be 8.35×10⁸m³/a.