Abstract: After well or reservoir sanding,critical sand transportation velocity is an important parameter for sand transportation design of vertical well bore.It can be worked out by adding a fixed coefficient of correction to the granule free settling terminal velocity.Based on theoretical and experimental analysis,the problem of shape coefficient measurement is solved through conducting granule settling experiment in virtue of the replacement of the equivalent diameter of equal volume by the equivalent diameter of equal sedimentation velocity.In addition,the formula of critical sand transportation velocity is established for the Dongying formation reservoir of Chengbei area through sand transportation test.The research results show that the correction coefficient of critical sand transportation velocity l increases with the decrease of the granule diameter in low viscosity fluid.It varies from 1.45 to 2.90 under conditions of the critical sand transportation experiment.These results are available to calculate the critical sand transportation velocity of no silting in vertical well bore of low sand grain concentration and can be referred to solve the sand transportation difficulties of vertical well bore in other areas.