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Elastoplastic models which have been developed in critical state framework show good capability in predicting soil behavior. In this paper, the effect of state parameter on improving the prediction of an elastoplastic constitutive model in state boundary surface framework has been studied. The original model, because of not considering the state of soil, ‘Dan be used only for a small range of stresses and void ratios for which the model has been calibrated. After evaluating and finding the deficiencies of the model using experimental results, it is modified to consider state of the soil. Evaluation of modified model shows that consideration of state of soil in the model has significantly improved its capability in predicting soil behavior.