Abstract: A detailed analysis of volcanic rocks reservoirs in the 5th and 8th districts of the northwestern Junngar Basin was done in this paper. The volcanic rocks comprise lava and volcanoclastics and are mainly distributed in the Jiamuhe Formation of the Permian. Based on the study on the well cores, rock thin sections and FMI it is shown that the average porosity and permeability of lava is 6.94% and 6.68×10-3μm2, respectively, and those of the volcanoclastics are 10.01% and 7.93×10-3μm2, respectively.The diagenesis of volcanic rocks includes cooling consolidation and devitrification at the earlier stage, and structural fracturing,dissolution and filling replacement at the later stage, which formed the secondary pores and fractures. The main influencing factors of reservoir quality include lithology, diagenesis and tectonics.