【Objective】The aim of this study was to investigate the proportion of dominant follicles（PDF）on HCG day in young and aged women.【Methods】In total，3 064 cycles of GnRH agonist long protocol and 918 cycles of GnRH antagonist protocol from 2014 to 2016 were retrospectively included. Patients were divided into 3 groups（low PDF，< 20%； medium PDF，≥20% and ≤40% ；high PDF，> 40%）. The measurements regarding the ovarian stimulation characteris? tics ，clinical pregnancy rate was compared between different PDF groups stratified by age and protocol. 【Results】 In patients aged ≤30 years who received the GnRH agonist long protocol，no significant difference was found in the clinical pregnancy rate between the different PDF groups（P > 0.05）. Regarding the GnRH antagonist protocol，no significant difference was found in the clinical pregnancy rate and moderate or severe OHSS rate（P > 0.05）. In patients aged ≥40 years， the clinical pregnancy rate in the low PDF group was higher than that in the high PDF groups（40% vs. 30.88%）in GnRH agonist long protocol. Concerning the GnRH antagonist protocol，patients in the low PDF group had a significantly higher clinical pregnancy rate than those in the other two groups（27.27% vs. 9.09% ，7.40% ；P = 0.002）.【Conclusions】PDF within 20% is recommended for older patients（≥40 years），especially in those receiving the GnRH antagonist protocol.