Five kinds of coarse cereals including highland barley， quinoa， oats， millet and mung beans were selected as subject in this study. The effect of different grain ratios on expected Glycemic Index（eGI） of extruded grains were researched by D-optimal mixture design experiments. Furthermore， changes of starch， amylose， protein， fat and dietary fiber of multi-grain cereal grains before and after extrusion were compared. The results showed that grain ratio had a great influence on the eGI of co-extruded powder， and the variation range was 60.77-76.45. Among them， the amount of millet has the biggest influence on eGI value， and it increases first and then decreases with the increase of the addition amount. The effect of highland barley， quinoa and oats on eGI value was the same， rising firstly and then declined with the increase of additive amount， while green beans showed the trend of first declining and then rising with the increase of additive amount. Through the determination of the nutritional composition of the extruded products with different ratios of cereals， the contents of starch， amylose， fat and protein were generally decreased after extrusion， and the contents of dietary fiber was increased overall after extrusion. And a significant negative correlation between GI and protein， dietary fiber， amylose， and resistant starch were observed.