Abstract: The runoff modeling in the watersheds where there is lack of hydrologicoal data is amportant and difficult prolbem in Hydrology. In this article, one hydrological model which can be used to model runoff in a watershed only using its geo-eferenced data based on a Geographical Information System was presented. In this model, the Runoff Curve Number method of SCS(Soil Conservation Service of American) was a used to calculate the generated runoff volume in a storm, and one revised unit hydrograph was proposed based on the triangular shape unit hydrograph of SCS and used to route the runoff into discharge at the outlet of thewatershed. In this paper, how to determine parameter values using geo-eferenced data of the watershed was discussed, and finally,the application of the model in the Dodder watershed of Ireland was intoduced as a case study.