To explore the prediction accuracy and physical properties of the grid water drop confluence method, and verify its applicability in areas lacking of or without data, based on the grid model of Xin’anjiang model, the flow yield calculation is carried out, and the confluence model based on the grid water drops is constructed. Tunxi and its nested basin in the humid area and Dongwan and its nested basin in the semi-arid area are taken as the study basins, and the nested sub-basin is assumed to be the area lacking of data. The simulation validation of Tunxi and the inner sub-basin of Dongwan is carried out without re-setting parameters, and the results indicate that in the same watershed, the comprehensive simulation accuracy of the grid water drop confluence model decreases with the decrease of the subwatershed area. The simulation accuracy of the model in Tunxi River basin reaches grade A and the simulation accuracy in its sub-basins basically meets the requirements, while the simulation accuracy of Dongwan reaches Class B and the accuracy of its sub-basins reaches Class C except for the pass rate of flood peak. This study validates the applicability of the grid-water-drop based confluence method in the area lacking of or without data.