Abstract: In order to know thoroughly the effects of pruning to promote trunk extension on 3-year-old Paulownia relative growth among branche,trunk and leaf,the annual growth dynamic processes of the base diameter Db and base cross section area Sb of branches from single branch to crown layers to the whole tree under 4 pruning treatments and control were measured and analyzed and futher simulated by Richards'functions.The results showed that:(1)the treatment of remaining 3～6 underlayer branches after pruning was optimal for promoting the branch growth.Under this treatment,the annual increments of Db and Sb in the upper crown may reach to 12.16～12.25 cm and 117.550～120.786 cm2,while in the lower crown the former to a mediate level and the latter to 107.748～113.291 cm2,thereby the annual increment of Sb of the whole tree reached to 228.535～230.841 cm2,being much higher than that of the control and other pruning treatments,as a result its total Sb reached to 287.907～294.535 cm2,being little higher than that of the control.(2) All of the annual growth dynamic processes of Db and Sb under treatments and control could be simulated reliably by Richards'function and their parameters of maximum annual increment A,maximum daily increment AGRmax,average daily increment Am,fast-growing period T,growing period Dg,and fast growing point,the initial and final time of fast-growing period were determined and analyzed.The analysis showed that the optimal treatment had relatively longer T and Dg,and maximized AGRmax(or Am) and A of Db in the upper crown which were 230.76%～240.19% and 234.93%～245.46% higher than that of the control,but got a moderate level in the lower crown.Meanwhile,compared with the control,the AGRmax(or Am)and A of Sb were 70.69%～78.78% and 35.85%～41.38% higher in the upper crown,while 105.43%～(127.17%) and 143.46%～155.86% higher in the lower crown,congsequently 61.95%～76.02% and 81.38%～(85.22%) of the whole tree.