Abstract: In order to research the effect of different production period on the birth weight of Australia merino offspring（the lamb who Australian merino ram fertilization Ordos fine wool sheep ewes）,four hundred pregnancy ewe were selected and randomly divided into four groups.Four groups of sheep ewes were impregnated in different months,and then the lamb birth weight after pregnancy ewe production was recorded.The results showed that the average birth weight of single lamb which was born in January,February,March and April in 2009 were（4.81±0.51）,（4.30±0.68）,（3.95±0.70） and（3.98±0.47）kg,while the double lambs were（4.03±0.85）,（3.08±0.24）,（3.08±0.53） and（2.87±0.40）kg,respectively.The average birth weight of single lamb which was born in January,February,March and April in 2010 were（5.43±0.63）,（4.63±0.55）,（4.60±0.73） and（4.54±0.63）kg,while the double lambs were（4.10±0.48）,（3.30±0.94）,（3.28±0.68） and（3.10±0.18）kg,respectively.Thereby,there was close relationship between birth weight and production period for Australia merino offspring.There was a decrease of birth weight for Australia merino offspring from January to April,among them the birth weight of lamb which was born in January was higher than that of lamb which was born in February,March and April,and there were significant difference in the birth weight of single lamb and double lambs which were born in January and April of each year（P 0.01）.