Abstract: The heterosis of phenotypic characters of Paulownia elite clone stem timber were studied with elite clone of P. tomentosa ×P. fortunei (TF33) and two standard trail varieties, P. fortunei (C001) and P. elongate (C125), as experimental materials. The results are as follows. (1)There were extensive and significant variation among characters at clone level among TF33, C001 and C125. (2)Three growth characters (height of stem-join, volume of stem-join and volume of main stem) and three trunk form characters (straightness of stem, stem-join form-factor and average taper of main stem) had high variation. The coefficient of variation (CV) ranged from 33.10% to 53.19%.2 (3)The height of stem-join factor played a vital role in influencing and determining general expression and total status of traits heterosis. (4)Straightness of stem was the key and bottleneck to the genetic improvement of P. tomentosa × P. fortunei on the stem form characters. (5)Most of the characters correlated very significantly or significantly and the correlations between different characters changed greatly. (6)TF33 had very prominent volume growth heterosis over C001. There was no remarkable heterosis compared with C125.