Abstract: The Haerjiawu formation in Malang sag in Santanghu basin is of variety of lithologies. Using logging crossplots can well identify its three types of lithologies such as vitric tuff, crystal?vitric tuff and lithic?vitric tuff. In plane, the sedimentary center of Haerjiawu formation is dominated by vitric tuff and crystal tuff, and toward sedimentary edge, the lithic content is increased and then transitional to volcanic rock. The reservoir space mainly includes primary pores, secondary pores and fractures, among which the intercrystalline pore in primary pores and dissolution pore in secondary pores are the main reservoir spaces, and micro?fracture can effectively improve the local reservoir’s percolation. The study shows that the vitric and crystal?vitric tuffs contain good physical property, but the vitric tuff is in limited distribution, and the lithic?vitric tuff is poor. The formation of Haerjiawu dense tuff reservoir is mostly controlled by mature source rock and favorable tuff reservoir distributions. The interbedded tuff in M2-M15well block has a good relationship of source?reservoir coexistence and could be the most favorable zone for petroleum exploration