The stress-strain relationship behavior of coarse grained soil was investigated through a series of large-scale triaxial compression tests. The test results show that the coarse grained soil would dilate under low confining pressure and contract under high confining pressure. Duncan-Chang model is not able to properly simulate such significant volumetric strain behavior of the coarse grained soil. A modified model of coarse grained soil is then developed through presenting new volumetric strain assumptions according to the test results. The model is convenient to practical application due to its simplicity in programming and few model parameters which could be easily determined with a similar approach as Duncan-Chang model. The validity of the modified model is preliminarily confirmed in predicting the volumetric strain response of coarse grained soil by triaxial compression test results of several kinds of coarse grained soils.