To meet the requirements of conducting a pilot study on surveying methods of ancient tree groups in Jilin Province,with the paired data of tree age and diameter at breast height (DBH) of 4,235 sample trees obtained from the 2nd National Census of Ancient and Notable Trees and the National Biomass Survey Surveying and Modeling Program,we developed DBH average growth models for individual trees of ten major tree species or groups (spruce,fir,Korean pine,larch,Mongolian oak,birch,elm,linden,aspen,and walnut) in Jilin Province by using the three common growth functions,involving Richards,Logistic and Gompertz,and the thresholds of DBH for identifying ancient trees of each tree pecie or group were determined.The results showed:1) Among the commonly used growth functions,the Richards function was found to be the most effective for fitting DBH growth models;2) The values of the coefficient of determination (R²) of the DBH growth models for the ten main tree species groups were all above 0.7,and the values of the total relative error(TRE) were within ±3%.The established models may be referred to determine the DBH thresholds of ancient trees and to estimate the age of ancient trees during the 3rd National Census of Ancient and Notable Trees in Jilin Province;and the modeling approach and the method for determining the DBH thresholds of ancient trees can be used as references for other provinces.