Abstract: The distinguishing grain size of coarse and fine particles is an important discriminant indicator for the seepage deformation type of cohesionless coarse grain soil. As the determination methods and the values are not unified, statistical analysis on seepage deformation testing results were taken with 62 sand samples from 7 projects to verify the suitability of different methods. The results show that the coincidence rate of the discrimination result and the testing result of seepage deformation is 93.55%when 2mm is used as the distinguishing grain size instead of d70d10, which is much higher than 51.61%. Thus, 2mm is recommended as the distinguishing grain size of coarse and fine particles for the non-uniform continuously graded sand.