Abstract: On the basis of the field research，drill core recording and rock and mineral identification，the main alteration types in Yili Mo deposit are divided into silicification，potassic alteration and sericitization，among which the silicification and quartz sericitization are closely related to mineralization. Meanwhile，the alteration zoning map in plane and profile are completed，mainly including two alteration zones of quartz-sericite-pyrite (phyllic alteration) and chlorite-epidote-calcite (propylitic alteration) which is characterized by superimposed hydrothermal alterations，comparing to characteristics of alteration zoning in typical porphyry deposits at home and abroad. That is to say，the early silicification has been superimposed by post quartz-sericitization and the latest carbonatization. According to these characteristics of alteration，the conclusion is that F4 fault might be a reverse fault controlling distribution of orebody，and implying a concealed Mo orebody existed in the fault footwall. According to the relationship of alteration and mineralization，the deep area in the southern section of the main mining area is the most promising molybdenum mineral exploration area.

Key words: Alteration zoning, Porphyry Mo deposit, Northern Great Khing'an ranges