Drift distance of riprap is a problem encountered frequently in works of river channel regulation,river regulation,bank protection,submerged dike construction and pier scour protection.Relying on 12.5 m deepwater channel phase Ⅱ project of Kou’an straight reach along the Yangtze River downstream Nanjing，a series of experiments have been conducted to investigate the effect of water depth,flow velocity,throwing height,rock mass and irregularly shaped foundation of rock on drift distance of riprap.Furthermore,a formula for calculating throwing distance of riprap is given based on hydraulic equilibrium equations which describes riprap movement by considering the vertical distribution of flow velocity.The coefficients in the calculating formula are obtained by curve fitting using the data from experiments.Reasonable agreement of calculated results with model experiment and field observation results verified the reliability of the model.