In recent years，the change of water and sediment in the Yangtze River has led to the intensification of bank erosion，and the underwater throwing revetment has become an important part of the renovation project.The new protective material bagged sand pillow comes into being，and the accuracy of its throwing drift distance prediction directly affects the quality and efficiency of the project.We take the regulation project of Baguazhou reach in Nanjing in the middle and lower reaches of the Yangtze River as an example，analyze the mechanism of water depth，flow velocity and sand pillow mass on drift distance，theoretically deduce the calculation formula of drift distance based on dynamics，and determine the formula coefficient by the field throwing tests under different flow velocities and water depths.The results show that the calculated values derived by the empirical formula in this paper are in good agreement with the experimental values，and the relative error is within 20%.