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The core observation and casting thin section authentication, combined with physical properties, scanning electron microscope, X-ray diffraction and mercury intrusion experiment, were employed to characterize the controlling factors on physical properties of Cretaceous Nahr Umr Formation sandstone reservoir in Halfaya oilfield. Iraq. The results show that the tide-controlled deltaic sandstone reservoir of core B of Nahr Umr Formation in Halfaya oilfield has medium porosity and permeability, and the reservoir space includes intergranular pore and dissolved pore; the pore throat changes greatly and the heterogeneity is strong; the controlling factors of reservoir physical properties include sedimentation and diagenesis; sedimentation affects pore space type and pore structure; reservoirs with good physical properties are developed with strong hydrodynamic conditions and good rock composition; diagenesis plays a significant role on the physical properties of reservoir; the compaction and cementation cause a large amount of pore filling, and the authigenic and clay minerals not only reduce the pore space, but also cause blockage of the throat, resulting in plugging of the pore throat and deterioration of the physical properties; the secondary pores produced by dissolution improve the reservoir physical properties; the highest-quality reservoir develops at the cross-laminated sandstone in tide-controlled distributary channel facies, and has the characteristics of large grain size, well sorting, relatively high content of quartz, low contents of clay mineral and cement, and large size of pore throat; the corresponding porosity and permeability are medium-high and high respectively, which are the focus of characterization and modeling of reservoir in the research area. [ABSTRACT FROM AUTHOR]