Abstract: Based on the two methods of Cobb-Dauglas production function and a comparison between mechanization and no mechanization in plant products industry, the estimating formulae of mechanization profit portion in plant products industry with gray-series forecast model were derived. Then the mechanization profit portion in plant products industry in Shaanxi Province was estimated quantitatively by above two methods from 1980 to 2000. The mechanization profit portion from the Cobb-Dauglas function is 20.79%, and the value obtained from the comparison method with mechanization and no mechanization is 21.10%. Finally, the evaluating results were analyzed and compared.