Abstract: In order to explore the effect of introducing Suffolk sheep on growth properties and slaughter performance of Valley-type Tibetan sheep under grazing conditions, in this experiment, fifty 3-month-old F1 generation of Suffolk sheep and Valley-type Tibetan sheep（hereinafter referred to as Suffolk-Tibetan hybrid sheep） with similar body condition and body shape and fifty 3-month-old self-bred Valley-type Tibetan sheep with similar body condition and body shape were selected and fed to 18 months. The weight of lambs at birth, 3, 7 and 18 months of age was measured and the daily gain of lambs was calculated. At the age of 7 and 18 months, 10 hybrid lambs and 10 Valley-type Tibetan sheep lambs with similar body weight（average population weight） were selected for slaughter. The body size indexes before slaughter and slaughter performance indexes was determined. The differences of above indexes were compared and analyzed. The results showed as follows: the body weight of Suffolk-Tibetan hybrid sheep at birth, 3, 7 and 18 months of age and daily gain of Suffolk-Tibetan hybrid sheep at birth to 3 months, 4 to 7 months and 8 to 18 months of age were significantly higher than those of Valley-type Tibetar sheep（P＜0.05）. At 18 months of age, the body height, abdominal circumference, chest circumference and hip height of Suffolk-Tibetan hybrid sheep were significantly higher than those of Valley-type Tibetan sheep（P＜0.05）,but there were no significant differences in body length, chest depth, chest width, hip length, hip width, tube circumference, forelimb length, hindlimb length, head length, head width and ear length（P＞0.05）. At 7 months of age, the body weight before slaughter, carcass weight, carcass length, eye muscle area, left half bone weight and left half net meat weight of Suffolk-Tibetan hybrid sheep were significantly higher than those of Valley-type Tibetan sheep（P＜0.05）, but there were no significant differences in bone/meat ratio and slaughter rate（P＞0.05）.At 18 months of age, the body weight before slaughter, carcass weight, carcass length and left half net meat weight of Suffolk-Tibetan hybrid sheep were significantly higher than those of Valley-type Tibetan sheep（P＜0.05）,eye muscle area was significantly lower than those of Valley-type Tibetan sheep（P＜0.05）, and there were no significant differences in left half net meat weight, bone/meat ratio and slaughter rate（P＞0.05）. At the age of 7 months, the liver weight and kidney weight of Suffolk-Tibetan hybrid sheep were significantly higher than those of Valley-type Tibetan sheep（P＜0.05）. At 18 months of age, the liver weight, lung weight, kidney weight and empty stomach weight of Suffolk-Tibetan hybrid sheep were significantly higher than those of Valley-type Tibetan sheep（P＜0.05）. At 7 months of age, head weight, blood weight, hooves weight of Suffolk-Tibetan hybrid sheep were significantly higher than those of Valley Type Tibetan sheep（P＜0.05）. At 18 months of age, the head weight, blood weight, hooves weight, skin weight of Suffolk-Tibetan hybrid sheep were significantly higher than those of Valley-type Tibetan sheep（P＜0.05）.In conclusion, compared with Valley-type Tibetan sheep, the Suffolk-Tibetan hybrid sheep have obvious heterosis under grazing conditions, and have the characteristics of fast growth, high growth potential, slow development and maturity, and high meat production performance.