Abstract: According as GB 265—88《Petroleum products—Determination of kinematic viscosity and calculation of dynamic viscosity)), kinematic viscosity of contaminated product of differential oil products is determined and the first-hand measured data is acquired.Error of computational formulae about contaminated viscosity which is put forward by Soviet Russia scholars is analyzed, and a new computational formula is proposed.Compared with other formulae, a new formula is applied to calculate contaminated viscosity and satisfactory results can be obtained.