For a progeny test, when analysis of variance is undertaken and heritabilities are calculated with plot means, the results of single tree heritability are not desirable. However, if carrying a plot means based analysis of variance with the within plot variances and the harmonic means of number of individuals per plot to be calculated separately, and then estimating the variance components and heritabilities, the results are similar to those which are estimated with individual observations even when the data set is of seriouse unbalance. A lot of computer resource and time can be saved under plot means based estimation. The data set from a field experiment was collected to show the detail method and process of this kind of analysis.