Abstract: 【Objective】 The purpose of this experiment is to study the growth and development rules of Yemili chickens and the correlation between body weight and body size indexes, so as to provide theoretical basis for scientific feeding and management of Yemili chickens. 【Methods】 A total of 200 Yemili chickens (half male and half female) aged 0 days in the same batch with good health condition were selected, and their body weight and body size data of 0-20 weeks of age were measured and recorded.After the fitting analysis of the growth curve of the weight of males and hens by Logistic, Gompertz and Von Bertalanffy models, the correlation analysis of body weight and body size was carried out based on the results of week age at inflection point. 【Results】 After 2 weeks of age, the body weight of cocks was significantly higher than that of hens (P < 0.01), and the growth peak of cocks and hens was reached at 8 weeks of age and 6 weeks of age, respectively.Logistic, Gompertz and Von Bertalanffy growth models all fitted the growth curve of Yemili chickens well, and the fitting degree was above 0.995, among which Gompertz model was the best one for the growth and development process of Yemili chicken body weight.In terms of body size, body oblique length, keel length, shin circumference, shin length, chest depth and back width of cocks at 2-20 weeks of age were significantly higher than those of hens (P< 0.01).The chest circumference of cocks aged 4-6 weeks was significantly higher than that of hens (P< 0.05), and that of cocks aged 8-20 weeks was significantly higher than that of hens (P< 0.01).The chest width of cocks at 6-20 weeks of age was significantly higher than that of hens (P< 0.01).In addition, correlation analysis showed that the body weight of 8-week-old cocks was positively correlated with body oblique length, chest depth, chest width and back width (P< 0.01).Body weight was positively correlated with keel length, chest circumference and tibial length (P< 0.05).The body weight of hens was positively correlated with keel length and breast width (P< 0.01).Body weight was positively correlated with body oblique length, chest circumference, tibial length, chest depth and back width (P< 0.05). 【Conclusion】 In conclusion, under the conditions of this experiment, the growth curve of Yemili chickens is nearly "S" shape, and the best fitting model for body weight growth rule is the Gompertz model.Body oblique length, chest depth, chest width and back width could be used as indicators for the early weight selection of cocks, and keel length and chest width could be used as indicators for the early weight selection of hens.