Based on analyses of thin section，core observation，logging and seism ic data，we studied the genesis of tuffaceous rocks and their reservoir features in the Permian Wuerhe Formation in Wuerhe Oilfield，Junggar Basin. The rocks can be classified into tuff，tuffites and tuffaceous sandstone and conglomerate and show high resistivity and low interval transit time in logging curves. The study shows that the sedimentary environment of the Formation is enclosed or semi-enclosed lake bay，and the sediments are composed mainly of volcanic ash and terrigenous clastics. Syngenetic high-salinity and alkaline water body provided favorable conditions for hydrolysis and alteration of the deposited volcanic ash. During the process，dolomitic tuffites were formed and analcite was precipitated. These rocks have different reservoir space（dual porosity media），including dissolved vugs，sluiceˉway and fractures. The dual porosity feature of the rocks improves the poroperm characteristics and controls the accumulation and distribution of hydrocarbons inWuerhe oilfied.