Abstract: The genetic variation of paulownia's natural stem-join characters was studied by means of field observation, field test and statistical analysis. The results were as follows: 1) Natural stem-join characters had extensive and obvious genetic variation at clone level of Paulownia. 2) Eight natural stem-join characters, which were height of stem-join, height of whole-stem, volume of main stem, volume of stem-join, volume of whole-stem, average taper of main stem, straightness of stem and witches' broom grade, had high variation. Their coefficient of variations (CV) were more than 30 (CV>30) and the CV change range was from 30.159 to 52.620. 3) Height of stem-join played an important role in influencing and determining total status and general expression of natural stem-join characters, straightness of stem played a vital role in genetic improvement of natural stem-join characters. 4) The paper preliminarily three classification standards about paulownia's natural stem-join types and proved that the continuous natural stem-join type was the most satisfactory type among all natural stem-join types. 5) The straightness of stem was not different, whereas other natural stem-join characters had extremely significant difference. 6) Natural stem-join characters had extremely significant difference among clones. 7) Many fast-growing hybrid clones had great heterosis in D.B.H., but their phenotypes of natural stem-join characters were very poor. Some hybrid clones had both powerful fast growth in D.B.H. and very excellent characteristic in natural stem-join. 8) Stem-join volume factor, main stem volume factor and average taper of main stem were respectively the first main composition,the second main composition and the third main composition and their total contribution rate was 75.91%. 9) "9501","9502"and "8508-2" belonged to the continuous stem-join type and had good phenotypes of natural stem-join characters, fast growth and anti-witches' broom. 10) Some important genetic parameters were simply calculated.

Key words: paulownia, natural stem-join character, genetic variation