Abstract: Since parallel models measure the efficiency of DMU without considering the environmental constraint in the selection of reference unit in DEA literature,the evaluation results subject to efficiency underestimation.In this paper,we improve the parallel model by taking into account the environmental attribute of DMUs,which adds practical significance to the obtained efficiency scores.Finally,the proposed model is applied to the efficiency evaluation of pollution control in China to demonstrate the rationality of the model.

Key words: environmental constraint, data envelopment analysis (DEA), parallel production system, effi-ciency evaluation