By collecting the elements of the water balance in the Taihu basin during 2010 -2015, this paper calculated andanalyzed the absolute errors and relative errors of the water balance. The main reasons of the errors were mainly the calculationaccuracy of the data that the variation on the water exchange, storage and consumption. Based on analysis of the factors in waterbalance, many measures were put forward to control errors, for instance, the construction of the monitoring abilities wasstrengthened and the estimation method of the water consumption was improved. These measures could reduce the errors of thewater balance and provide more accurate data foundation for the water allocation plan in the Taihu basin.