The authors carried out a N enrichment experiment in Wuyi Mountain with four N addition levels (control (0), low N (50 kg N/(hm²·a)), medium N (100 kg N/(hm²·a)) and high N (150 kg N/(hm²·a))) This study was designed to study the seasonal characteristics of DBH (diameter at breast height) growth of Castanopsis carlesii and its short term response to simulated nitrogen deposition. Results show that the Castanopsis carlesii annual growth can be divided into 3 periods: water recovery period, fast growth period and slow growth period. N additions play different roles on the growth of Castanopsis carlesii. In the fast growth period (June to October), low N and medium N significantly increase the relative growth rate of annual DBH. Relative DBH growth in slow growth period (November to April) has no significant response to N addition. Among different diameter classes, N additions affect the DBH growth differently: low and medium N additions significantly promote growth in low diameter class (5 cm<DBH<15 cm) (p<0.05), but the tree growth has no significant response to high N addition. With the increase of tree diameter, the DBH growth of Castanopsis carlesii decreases sensitivity to N additions. High diameter class (DBH>25 cm) does not show significant response to N deposition. The study also finds that medium N addition significantly increase the biomass growth rate of Castanopsis carlesii in the study area (p<0.05).