The interlayers in carbonate reservoirs had various genesis. They were difficult to identify effectively by the logging because of their highly hidden, which had great influence on the efficient development of reservoirs. Taking the bioclastic limestone of the Cretaceous Mishrif Formation in the M oilfield of Iraq as an example, the interlayers were identified by core observation, casting thin section and physical property data. The distribution of well logging values of different types of interlayers was defined by rock-electric fine calibration and the most representative log of different interlayers was selected. Under the controlling of interlayers genesis, different interlayers in uncoring well was interpreted. The results showed that there were five categories in the Mishrif formation in M oilfield which were the restricted deposition type, the deep water deposition type, the weathered and cemented type, the leaching and cemented type and the restricted exposure type. The radar chart was used to compare the log characteristics of different interlayers, and the “false judgment rate” was used to characterize the discrimination ability of different logging between the reservoir and the interlayer. It concluded that the reservoir and interlayers could be effectively separated by the density value of 2.55 g?cm-3. Under the control of facies, the leaching and cemented interlayers was identified by a density value of 2.45 g?cm-3or a sonic curve value of 70μs?m-1 inside the shoal reservoir. The restricted exposure interlayer and the weathered and cemented interlayer were preferentially identified among the interlayer by gamma value of 80 API and density value of 2.65 g?cm-3 respectively. Under the control of stratigraphic unit, the deep water deposition interlayer was identified in the MB2.2 layer, and the restricted deposition interlayer was identified in the MA, MB1 and MB2.1 layers. Different interlayers had different distribution law and barrier properties, and the study results could provide basis for the separated development of thick carbonate reservoirs.