The Mishrif Formation（Upper Cretaceous age）is an important carbonate reservoir in the Persian Gulf Basin. Taking Y oilfield in southeast Iraq as an example，a comprehensive study on carbonate reservoir and its logging response was carried out with core description，thin section observation，petrophysical analysis，mercury injection and well logging data.The results are as follows：there are bioclastic grainstone，reef limestone，packstone，wackstone，dolomitic limestone and mudstone developed in the Mishrif Formation；the types of storage space in the carbonate rocks include intergranular pores，moldic pores，intragranular pores，intercrystal pores and intergranular micropores，and dissolved fractures and pressure-solution fractures also developed in partial sections；the main range of reservoir porosity derived from core analysis varies from 8 percent to 28 percent，and permeability ranges from 1 millidarcy to 100 millidarcy. The pore system of Mishrif carbonate rocks is constructed by four combinations of pore types：intergranular-moldic pores，intergranular-intragranular-intercrystal pores，intergranular-intercrystal pores，and micropores-moldic-intercrystal pores. The highquality reservoirs are characterized by low gamma ray value，high acoustic value，high neutron porosity，low density and high resistivity. The highquality reservoirs in Mishrif carbonate in the study area are closely related to regressive cycles and are controlled by original depositional environment. Syngenetic selective dissolution，exposed dissolution and cementation in burial period are important controlling factors of reservoir qualities.