Abstract: Some shortcomings in one-dimensional heat transfer model of thermal conductivity are found.A more rigorous three-dimensional heat transfer model is proposed.With more scientific consideration of sidewall cooling effect,a new formula of calculating thermal conductivity is developed.The rationality of the new formula proposed is proved by carrying out the experiment with rubber disks.An impact factor P that describes the degree of sidewall cooling effect is introduced and found to rise with the increase of the sample＇s thickness.

Key words: thermal conductivity, steady-state method, three-dimensional model, cooling effect