The flow of water through a certain location in a river is a necessary data for disaster prevention, water resources and environment assessement. Flow measurement often requires a lot of manpower and equipment. Therefore, on a river system, several locations are investigated and surveyed to set up a hydrological station. Flows in sub-basins without hydrological stations are usually calculated by hydrological models, such as: MIKE NAM, TANK, HEC HMS… This paper will present the application of MIKE NAM model to simulate daily flow for the Quy Chau and Hoa Quan basins. The results of model calibration and validation have identified a set of parameters with a fairly high Nash-Sutcliffe efficiency (NSE), greater than 0.70, indicating a good model performance. The calibrated parameters can be applied to calculate the daily discharge for similar sub-basins of the Ca river.