Abstract: Duncan Chang model includes eight parameters.According to tests,data analysis and computation,besides k the other seven parameters vary within limits of 10%～40%,and cause 10～100 percent variety of computed displacements.While the k value may be changed to ten times because of measurement accuracy,the displacements will be also changed within ten to hundred percent.In the example of an earth dam with height of 31 m,the changes of the displacements and stress ratio are computed with each of the parameters increased or decreased 20 to 25 percent from test data.The results can be used as reference for test of model parameters and analysis of computed results.