Taking Xiaomi beach as a study case，we carry out the site investigation and simulate the fluid flow by the software CFD (FLUENT 6.3.26) to seek the reasons for the washout of the dike root.The result shows that the damage causes of the spur dike’s root in the upper reaches of the Yangtze River may be the influence of river terrain’s deflecting flow on the velocity of the dike root.We thus propose the protection measures including siting the spur dike as far to the flow erosion area as possible，reinforcing the dike root or embedding the root into the bank slope，etc.