Abstract: In order to perfect the second generation of GI technical standard system, GI value of roughage and the milk yield were taken as parameters to set up the forecast model of the best supply level of concentrate in the diet of diary cows. 36 healthy Chinese Holstein cows in middle lactation stage were selected and randomly divided into 3 big groups （ with 3 groups in each big group, with 4 cows in each group ） according to the principles of with the same milk yield ,lactation period and similar fetal times. In the first big group ,yellow corn silage was used as roughage and the ratio of concentrate to roughage was 55：45,57.5：42.5 and 60：40 respectively, named as A1, A2 and A3. In the second big group, yellow corn silage and A neurolepidium chinense were used as roughage and the ratio of concentrate to roughage was 55：45,57.5：42.5 and 60：40 respectively, named as B1 ,B2 and B3. In the third big group,whole corn silage and A neurolepidium chinense were used as roughage and the ratio of concentrate to roughage was 55：45,57.5：42.5 and 60：40 respectively, named as CI ,C2 and C3. The effects of different roughage level （GI） and different concentrate supply level on the production performance of lactating dairy cows were studied. The results showed that lactoprotein, lactose and milk yield showed increasing trends and milk fat showed a decrease trend with the increasing of concentrate proportion. The ratio of concentrate to roughage had significant effects on milk yield （P〈0.05）and had some influences on milk composition （P〈0.05）. With the increase of roughage quality （GI）, milk fat and milk yield showed an increasing trend, and lactoprotein and lactose decreased, but its effects on milk fat, lactoprotein and lactose were not significant （P 〉0.05 ）, the effects on milk yield was significant （P〈0.05）.