To solve the problem of obtaining river terrain data in ungauged area, a new method for extracting river terrain data based on Google Earth image was proposed. Using this method, the river terrain data of Jianjiang River Basin are extracted, and a one-dimensional hydrodynamic model was constructed based on those river terrain data. The results show that the simulation process by the hydrodynamic model based on river terrain data extracted by this method is basically consistent with the actual process. The relative errors of the maximum and minimum flow rates are 14.3% and 7.8%, respectively, while the overall relative error of flow simulation is 13.2%. The relative errors of the simulated maximum and minimum water levels corresponding to the measured ones are 5.5% and 3.9%, respectively, while the overall relative error of water level simulation is 5.2%. It shows that extracting river terrain data based on Google Earth image is a convenient and effective method to solve the problem in the area without river terrain data.