The resources of ultra-lowpermeability reservoir are abundant，but for the poor reservoir properties and strong heterogeneity, the development is difficult. According to comprehensive research of sedimentary microfacies and diagenetic facies, it is suggested that there are areas with relatively high porosity and high permeability in ultra-low permeability reservoirs. Due to the good clastic sorting, low content of matrix and poor compaction and cementation during the early diagenetic stage, pores can be well preserved. For the active fluid motion, intensive denudation and dissolution in the later diagenetic stage, delta front subsea distributary channel microfacies and braided turbidite channel microfacies are the favorable reservoir facies belt. This cognition is significant for optimizing hydrocarbon enrichment area and promoting economic development of ultra-lowpermeability reservoir.