Distributed hydrologic model is a kind of developing method of hydrologic modeling, so its ability of describing the spatio-temporal distributing of runoff is not enough now. This study is about increasing the precision of spatial describing and simulating catchments and runoff. One of the keys is about extracting carriers of runoff routing, such as routing paths, digital water system, and so on. Another is about the runoff generation and routing grid to grid based on digital catchment.In order to resolve the problem of extracting better catchment characteristics in plains, grid electronic river network is inducted in digital elevation models as assistant data sources to determine flow vector of each grid, which is called grid-channel method. Catchment properties gotten with this method were compared with that gotten only from digital elevation models. It proved that the problem about extracting catchment properties in plains could be solved well with the new method. It was compared with other similar methods, too. A conclusion was drawn that the precision of extracted catchment properties gotten with the new method is better for it had not change values of digital elevation models.The parameter of extracting digital river networks, called contributing area threshold or critical contributing area, was studied, including its effects on basin runoff routing and the methods to determine it. A new method was used by comparing drainage density, headwater density and water-system fractal dimension of digital river network with that of factual river network to determine the parameter. 60 samples distributed in Sanmenxia-Huayuankou interzone of Yellow River were studied. And their thresholds were analyzed to seek the distribution laws of contributing area threshold.A method of runoff routing grid to grid in digital basins was studied based on hydraulics equations. Digital slopes and channels were generalized in order to using traditional hydraulics methods in digital basins. The spatio-temporal change of basins and runoff was described by the change of some parameter. Kinematic wave was chosen to simulate slope routing and Muskingum-Cunge method was chosen to simulate channel routing after analyzing characteristics of digital basins.A frame of grid distributed hydrologic models was established based on upper studies. It can outlet the flood process of each grid and can simulate the spatial inhomogeneity of their effects on flood. In order to simulate the spatial distribution of generation process, SCS-CN method was used to calculate generation runoff of each grid for the spatial change of underlying surface can be expressed in its parameter CN and its conference value is developed maturely. Some amend was done for SCS-CN to solve the problem of parameter transplant.And 9 floods of upper Qin River, which is controlled by FeiLing gauge, were simulated with this distributed model. The conclusion proved that it could simulate the runoff of basin outlet well. The simulated runoff process of Kongjiapo gauge, which is lying upper of Feiling gauge, was compared with observed, too. It was found that its precision is lower than that of Feiling gauge. The reason may be that the parameters could not describe the spatial change of underlying surface accurately. So more studies on spatial variability of parameters for both generation and routing should be necessary.