Abstract: In rock engineering,alteration usually causes various engineering geological problems. The microscopic characteristics and physical and mechanical properties of altered rocks in a deep buried long tunnel in northern Xinjiang were studied,and numerical simulations were performed for the altered rock tunnel section. The results show that the rock alteration type of the tunnel surrounding rock is chloritization of black mica and clayification of potassium feldspar. The concept of alteration index is proposed using the chlorite content and clay mineral content in the altered rock. The macroscopic characteristics of the altered rock are combined to classify the alteration degree. As the degree of alteration increases,the water absorption,and porosity of the rock subsequently become larger,and the bulk density,saturated uniaxial compressive strength,elastic modulus,and deformation modulus decrease substantially. The engineering example simulation found that the displacement of tunnel surrounding rock is increased significantly with the enhancement of rock alteration,revealing that the alteration effect has a great influence on the deformation and damage of surrounding rock. The research results have a certain reference value for similar projects in eroded rock areas.