Abstract: The cohort study method was used to collect breast milk from 3~5 d,12~14 d,1 month,2 month,3 month,4 month and 6 month postpartum in north China and south central region,respectively,in order to investigate the dynamic changes of fat,protein,lactose,dry matter,total energy and true protein in breast milk of Chinese healthy lactating women at different lactation stages.At the same time,the relationship between the mode of delivery and the sex of the baby and the macro nutrients concentrations was analyzed.The MIRIS HMA milk analyzer was used to analyze macro nutrients concentrations in breast milk.The results showed that in colostrums,the total protein and true protein content of spontaneous labor group were higher than cesarean section group( p < 0.05).In transitional milk,all macro nutrients concentrations were not affected by the mode of delivery( p > 0.05). In mature milk( 6 month),the lactose and dry matter content of cesarean section group were higher than spontaneous labor group( p < 0.05). Furthermore,in colostrums and transitional milk,all macro nutrients concentrations were not affected by the sex of the baby( p > 0.05),but in mature milk,the fat and total energy of 3 month and protein and true protein of 4 month content of girl group were higher than boy group( p < 0.05).The content of macro nutrients in breast milk related to the mode of delivery and the sex of the baby.