【Objective】To compare the effect of the conventional controlled ovarian stimulation（COS）and mildstimulation protocol in poor ovarian responders（POR）undergoing IVF/ICSI.【Methods】Aprospectiver and omized study was performed in 191 patients with POR undergoing in vitro fertilization（IVF）or intra cytoplasmic sperm injection（ICSI） .  The patients were randomized into two groups，modified long protocol was applied in COS group，while letrozole compensated with low dose gonadotropin protocol was applied in mild stimulation group. The clinical outcomes were compared between the setwo groups.【Results】Comparing with COS group，both endometrium thickness and serum E2 level on the trigger day were significantly lower in the mild stimulation group［（9.6±2.5）vs（11.4±2.5）mm， （560±470）vs（1200± 710）pg/mL，P<0.05］. No significant difference was found between the two groups in the serumLH and Plevels on the trigger day（P>0.05）.Although the number of oocytes retrieved［（4.1±2.8）vs（2.8±1.9），P<0.05］and the number of available embryos［（2.0±1.6）vs（1.5±1.4），P<0.05］were significantly higher in the COS group，similar embryo implantation rate，clinical pregnancy rate perembryo transfer，per OPU and perinitiation cycle，abortion rate and live birth rate were observed in bothg roups.【Conclusion】For POR patients，the COS protocol and the mild stimulation protocol yield a similar clinical pregnancy rate. Considering the fewer Gndosage and shorter ovarian stimulation lengtha ssociated with the letrozole mild stimulation，it can be concluded that the letrozole mild stimulation protocol is an ideal ovulation induction regimen for POR patients.