Abstract: Based on the data analysis of casting lamella，scanning electron microscope and Xdiffraction，the authors hold that Yongjin area Xishanyao Formation sandstone reservoir diagenesis includes compaction，cementation and dissolution.Because the plasticity lithic sandstone is the main component，the compaction lowers the reservoir porosity，which is the main damaging factor of the reservoir physical property.The dissolution improves the reservoirs physical property to some extent and could higher the porosity up to 7%.On the basis of the study above，the conclusion is reached that the facies control the distribution of the reservoir and have some influences on the compaction and dissolution，so beneficial facies belt is the base of good reservoir.On the other hand，high abnormal pressure of oil/gas generation and hydrocarbon emplacement occurred at early stage could prevent the lithologenesis，to some extent improve the reservoir porosity，and provide interspace for hydrocarbon accumulation.

Key words: Junggar Basin, sandstone reservoir, diagenesis, abnormal pressure, Xishanyao Formation 