Abstract: The four kinds of alfalfa hay, selenium rich type, selenium-cobalt rich type, selenium-eobah-zine rich type and common type, were added up to cow diet to determine their effects on growth and production performance of cow, The results showed that affalfa hay of rich selenium could not only enhance body length , heart girth and body weight compared to common alfalfa hay, but also daily milk yield could increase by 8.6 %, the feed to milk ratio decrease by 12.17 %, and the conversion and utilization rate of feeds also have been improved. Meanwhile Alfalfa hay of rich selenium-cobah could markedly raise fat content of milk reaching 22.15 %, content of protein, lactose and solid not fat respectively increase by 9.28 %, 3.26 % and 4.69 %. In milk practical production, specific alfalfa hay of rich selenium should be chosen to be added up to diets according to the demands.