The deviatoric stress calculating process of triaxial consolidation test is based on the assumption that the sample always keeps a cylinder shape with equivalent volume and the cross sectional area of the sample is equal at any location during the test. But in actual test the sample is drum shape in the test process due to end effect, which is inconsistent with the assumption. We deduce the deviatoric stress calculation formula according to the actual situation of sample deformation in consolidated drained triaxial test. Results show that different with that in specification, the value calculated from deduced deviatoric stress formula according to the actual deformation changes in a scope, with the minimum value lower and maximum value higher than standard value. By calculating dam subsidence, we also give the recommended value of deviatoric stress in coarse-grained soil’s triaxial consolidated drained test.