Abstract: the essence of the washout mechanism of subgrade for highway along the river, is a process of interaction impact that bedrock scour resistance of soil and subgrade near wall. From the perspective of hydraulic analysis get the flow shear stress is the power source along the river embankment washout, again from the force balance principle, analysis of washout airport on the surface of the soil under the weight of the failure mechanism. According to the practical engineering calculation example to verify this method, the results show that the predicted results compared with the truth. Research on highway roadbed along the river washout prevention and control of waterlogging prediction has positive significance.