Biot number (Bi) is required smaller than 0.1 during computation of transient state heat conduction with lump heat capacity method. Using the theory of the lump heat capacity method the analytic solution of large\|scale barrel steel ingot under the conduction of unsteady state heat conduction was discussed. Comparing the estimated data of the analytic solution and the empirical data, the result is very well matched. The method can be used in the computation of object heat conduction with the lump heat capacity method when Biot number is far bigger than 1.