Abstract: The paper aims to acquire the growth condition and improve investigation efficiency of Fraxinus in the urban area of Beijing, and study the DBH growth estimated model. The author used random sampling method, collected the growth index of Fraxinus in the urban area of Beijing, such as DBH, tree height, under branch height, crown width, leaf area, and classified these indexes according to DBH class, constructed the estimation model of DBH and multiple growth index by using 5 kinds of single factor model. The results showed that middle diameter class of the Fraxinus were most widely used in street trees, accounting for more than 63% of the total; the correlation of DBH and height were the highest, followed by the crown width, leaf area, clear length. The best model of DBH and height was H=98.2399-28.0859D 2.8115D²-0.0743D³, whose correlation coefficient was 0.9967 and standard error was 0.3299%. The better choice of the estimation model among DBH with other multiple growth index was: D=0.5595H²-9.6656H 2.0172h²-9.2454h-1.0413W² 12.4859W-0.0188S² 1.4996S 6.2011. The standard deviation was only 1.0242, while the accuracy was up to 95.61%. The DBH growth estimation model of the wax street trees established in this study had good effect and suitable for trees of all ages, and could provide a theoretical model with fast investigation and data update for growth status of Fraxinus, landscape quality and ecological benefit in the urban area of Beijing.