Abstract: While polymer solution flows through the capillary of Ubbelohde viscometer,the adsorption of polymer molecules on the surface,sometimes,seriously changes the physical and chemical properties of the surface,especially when electrolyte is added into the solution.The effective diameter is narrowed.Thus,time for blank solution to flow through the capillary is different before and after measuring time of the solution with varied mass concentration,making the average molecular weight strikingly different.Despite importance of the time for blank solution,no uniformly adopted method has been established to determine it.However,for the currently used methods,η<SUB>sp/</SUB>ρ/ρ is no longer the linear function&nbsp; ρ as the concentration decreases.To make the linear correlation again,a solution of a wide range of low mass concentration was prepared (5.0×10<SUP>-4</SUP>～5.0×10<SUP>-3</SUP> g/mL),and addition of electrolyte was considered.A method to determine the time for blank solution was proposed.Theoretical analysis and experimental data of polymer molecules in solution containing electrolyte showed that this method is more applicable and accurate,makingη<SUB>sp/</SUB>ρ/ρ the linear function of ρ &nbsp;at wider range of low concentration.<BR>