Abstract: The reproductive performance of sows is one of the main production indicators for pig farms. There is a significant correlation between back fat thickness and reproductive performance of the sow. To study effects of back fat thickness on reproductive performances of sows at different stages of gestation period by regulating, the new French Large White pig from Wens breeding pig company were chosed as subjects. The back fat thickness and reproductive performances were measured at different stages of gestation period. The best reproductive performance of sows appeared in early pregnancy and mid-pregnancy with back fat thickness regulation range of -2 to 3 mm. The best reproductive performance of sows appeared in late pregnancy with back fat thickness regulation range of -2 to 0 mm. Back fat thickness of sow keep in a appropriate range, which can improve its reproductive performance and increase benefits of pig farm.