Since ruminants needs a constant adaptation to the environmental changes, therefore they adapt different ecological niches and feeding habits. In addition the morphology and function of digestive system also reveals some adaptive evolutionary characteristics. Blue sheep (Pseudois nayaur) display a variety of morpho-physiological adaptations–typical for grazers. We collected 64 adult blue sheep samples (whole animal carcass) in different seasons from the Helan Mountains, China. The external morphological parameters, digestive system morphological indexes and rumen surface enlargement factor were determined. Our results revealed that the weight of rumen and reticulum was positively correlated with body weight (P = 0.004), while the food channel aperture, intestinal length and weight of blue sheep digestive tract have no significant difference between different seasons (P > 0.05) and gender (P > 0.05). Therefore, it is difficult for blue sheep to delay the flow rate of large food particles in the rumen and reticulum by adjusting the aperture of the mesh flap. There were significant differences (P < 0.001) in the density, length and width of mastoid for blue sheep, and the rumen mucosal surface dilatation coefficient was 2.85 ± 1.37, which is the typical characteristic of roughage feeders. The nutritional and ecological characteristics of blue sheep are the obvious morphological and physiological adaptations to the herbivorous diet. They can adopt the quick foraging strategy for consuming large amount of food and rapid excretion to obtain the energy needed for their activities and to better adapt with the environmental changes.