[Objective]Analysing the effect of body size indexes on body weight of Kirghiz sheep males and females at three stages:newborn,weaned and 8 months old.[Methods]372 newborn lambs,321 weaned lambs and 223 8-month-old lambs were randomly selected,totalling 916 lambs,and their body weights(Y)were determined along with body length(X1),body height(X2),chest circumference(X3),tube circumference(X4)and other body size indexes,and the correlation,pass-through and multiple regression analyses were carried out on the data of each stage by using SPSS.27,so that the correlation between body weights of Kirghiz sheep and their body sizes at different stages could be established.The optimal regression model of body weight and body size of Kirghiz sheep at different stages was established.[Results]Body length,body height,chest circumference,tube circumference and body weight at each stage(newborn,weaning,8 months old)were positively correlated with the body size indexes of Kirghiz sheep males and females(P<0.01).The body size index with the largest direct effect on body weight at different stages was chest circumference,followed by tube circumference and body height.The direct and indirect effects of chest circumference on body weight were greater than those of the other three body-size indicators.[Conclusion]The regression equations at different stages can be used in the early selection and breeding practice of Kyrgyz sheep,moreover,in the process of growth and development of Kyrgyz sheep,it is necessary to pay attention not only to the selection of body weight,but also to strengthen the selection of body size indicators.