Abstract: A main idea of comprehesive Assessment of atmospberic environmental quality is described by using sets pair analysis. The formula is presented for the calculation of synthetic degree of identical, synthetic degree of discrepancy, syntberic degree of contrary in the I.D.C. commexion formula of multicontaminants. The results of comprehensive assessment of atmospheric environmental quality in Chengdu during 1982-1987 by this method coincidr with practical cases.