Carbonate reservoirs are characterized by strong heterogeneity and complex pore throat structures，with poor correlation between porosity and permeability. Typical porous carbonate reservoirs develop in the Cretaceous Mishrif Formation in the Middle East，with the permeability differing by three orders of magnitude under the same porosity，bringing a huge challenge to accurately evaluate permeability and properly categorize reservoirs. To deeply analyze the key controlling factors of permeability in porous carbonate reservoirs of the Mishrif Formation in the Middle East，we find different models of pore throat structures coexist in the carbonate reservoirs of the research area through 415 MICP samples from the M Oilfield. To be specific，porosity and permeability correlate much better in a uni-modal pore throat structure than in bi-modal and multi-modal structures. Then the characteristic parameters of pore throat structures are analyzed quantitatively to explain the regularity in porosity and permeability of carbonate reservoirs with a multi-modal pore throat structure when the parameters of the pore throat structure are changed. Results demonstrate that the pore throat radius（R20），corresponding to 20% mercury injection saturation，correlates best with permeability. With R20 as the characteristic pore throat radius，its correlation study with porosity and permeability reveals that porosity first increases linearly with the greater R20 and then remains stable，while permeability keeps rising with the growth in R20.