Abstract: The Grey System Theory is applied on reservoir evaluation.Firstly,the pedigree cluster analysis is used to choose relatively independent parameters.For reservoir evaluation,6 parameters,including thickness of sandstone,ratio of sand body,shale content,variation coefficient,porosity and permeability,are selected from 9 parameters of reservoir.At the meantime,the Grey System Theory correlation analysis is applied to confirm various weight coefficients.Based on the calculation of reservoir comprehensive evaluating values,critical point analysis is used to determine the threshold value of comprehensive reservoir evaluation.The comprehensive reservoir quantitative evaluation is conducted on Chang-6 oil-bearing layers in the Midwest Ordos Basin.The submersed distributary channel sand bodies of delta front are mainly Type Ⅰ and Type Ⅱ,and the submersed distributary channel wings are mainly Type Ⅲ.