【Objective】To investigate the effects of different doses of gonadotropin releasing hormone agonist（GnRH-α） on the down-regulation of normal ovarian reserve，and compared the down-regulation level as well as the clinical outcome of in vitro fertilization and embryo transfer（IVF-ET）cycles.【Methods】This RCT study included 63 infertility couples of age<35 yrs. women with normal ovarian reserve function who were intended to received GnRH-α long protocol treatment. Of the 63 women were randomly divided into three groups according to the dose of triptorelin，21 received daily 0.05 mgshort-acting GnRH-α，21 received daily 0.1 mg short-acting GnRH-α，while 21 received reduced -dose depot of 1.25 mg GnRH-α.【Results】In the three groups，the average duration of down-regulation reached after injection of GnRH- α，the level of LH and E 2 ，the total number of antral follicles，the number of antral follicles of <4 mm and 8~9 mm were similar. The serum follicle-stimulating hormone level on the day of gonadotropin initiation were significantly higher in the two short-acting groups compared with the long-acting group［（3.92±1.12）U vs.（3.03±1.14）U vs.（2.05±1.12）U，P< 0.001］. Four hours after the GnRHa injection，the serum FSH，LH levels were higher in short-acting 0.05 mg group than the short-acting short-acting 0.1 mg group. Both number of days of gonadotropin stimulation and gonadotropin doses were similar in three groups. On the day of hCG administration，the numbers of 14-18mm diameter follicles［（3.91±2.12）vs. （5.81±3.55）vs.（6.43±3.39），P<0.001］as well as the proportion of follicles with diameter ≥18 mm/≥10 mm［（33.1%± 13.2%）vs.（24.0%±12.4%）vs.（30.1%±12.2%），P<0.05］，were both statistically significant different in three groups. Although serum LH level on hCG day was significantly increased in 0.05 mg group［（2.47±1.33）U vs.（1.80±0.69）U vs. （1.43±0.53）U，P<0.05］. No premature LH surge and premature ovulation was observed. The number of retrieved oocytes was significant different［（10.14±4.80）vs.（11.51±2.42）vs.（12.79±2.73），P<0.05］. However，no significant differences was found regard to the number of MII oocytes，and the serum estrogen level per egg was significant higher in 0.05 mg group［（282.33±42.13）U vs.（221.62±32.02）U vs.（200.03±37.89）U，P<0.001］. The live birth rate（LBR）of these three groups in fresh cycles were 61.9%，55.0%，and 50.0%，respectively. The cumulative LBR were 85.7%，76.2%， and 75.0%，respectively.A increased trend was observed in the clinical pregnancy rate，cumulative clinical pregnancy rate and cumulative LBR in 0.05 mg group than the other two groups.【Conclusion】For women with normal ovarian reserve，as the GnRH-α dosage decreased，the down-regulation of pituitary reduced，while serum LH levels on the day of hCG trigger increased. The number of oocytes retrieved was decreased，the proportion of cycles which retrieved ＞15 oocytes was also lower. However，the average estrogen level per egg was significant increased，and a better clinical out? come of IVF-ET was received.