Abstract: In order to carry out trunk extension by lateral buds,the relationship between branching sprouted from lower lateral buds and trunk extension sprouted from upper lateral buds was investigated in 1-year-old seedlings of Paulownia tomentosa × P.fortunei 33 under natural conditions.The results showed that there was a close relationship between branching sprouted from lower lateral buds and trunk extension sprouted from upper lateral buds in a high density.The branching sprouted from opposite lateral buds was unfavorable to trunk elongation, and it decreased the form quotients of extending trunk.The smaller the obliquities of branching by the first pair of lateral buds were,the larger the form quotients of extending trunk were.At the same time,the growth of the first and second pairs of branching could accelerate the growth of DBH.The branching obliquities by the third pair of lateral buds were negatively correlated with the upper diameters of main trunk and the base diameter of extending trunk.The length of extending trunk and the upper diameter of main trunk increased with the increase of branching number and the dedine of single branch growth.The length and diameter of branches sprouted from the fourth pair of lateral buds were positively correlated with the diameter of the trunk,and the fifth lateral branching was correlated with DBH,while there was a little influence of lateral branching below the fifth on the growth of main trunk and extending trunk.