To compare the clinical outcomes and endocrinological characteristics of progestin-primed ovarian stimulation (PPOS) protocol using medroxyprogesterone acetate (MPA) 8mg versus 4-6mg daily in POSEIDON group 3 and 4. This was a retrospective cohort study. Low-prognosis women from POSEIDON group 3 and 4 using MPA high-dose(8mg/d) or low-dose(4-6mg/d) in PPOS protocol who underwent IVF/ICSI at the Reproductive Medicine Center of the First Affiliated Hospital, Fujian Medical University from February 2019 to February 2022 were recruited. The primary outcome measure was the incidence of premature LH surge. The secondary outcome measures included the embryo results and clinical pregnancy outcomes. Baseline characteristics of patients were similar in the MPA high-dose(8mg/d) group and MPA low-dose(4-6mg/d) group both in POSEIDON group 3 and group 4. In POSEIDON group 3, there was no significant difference in the incidences of LH surge between the high-dose group and the low-dose group (11.1% vs. 6.8%). No significant differences were observed in the number of oocytes retrieved (4(3,6.25) vs. 5(3,7)), viable embryos (2(1,3) vs. 1(1,3)), clinical pregnancy rate (52.3% vs. 52.5%) and live birth rate (43.2% vs 42.5%) per transfer cycle between the groups. In POSEIDON group 4, the incidence of LH surge was similar between the high-dose group and the low-dose group (6.9% vs. 6.3%). No significant differences were found in the number of oocytes retrieved (3(2,5) vs. 3(2,5)), viable embryos (2(1,2) vs. 1(0,2)), clinical pregnancy rate(34.6% vs 31.9%) and live birth rate(17.3% vs 21.3%) per transfer cycle between two groups. MPA started at 4mg daily and then increased to 6mg daily was as effective as MPA 8mg daily in preventing an untimely LH rise in low-prognosis women from POSEIDON group 3 and 4. PPOS using MPA 8mg or 4-6mg daily was comparable in terms of the number of oocytes retrieved and pregnancy outcomes after FET.