The Upper Cretaceous Mishrif Formation in the HF Oilfield of Iraq developed in the carbonate gentle slope of the passive continental margin of the Neo-Tethys Ocean. It is still not clear that the sedimentary facies are affected by sea-level change. Based on the observation and analysis of cores and thin slices, the lithology and sedimentary microfacies characteristics of MB1-2 layer in the Mishrif Formation of HF Oilfield are studied. The results show that the interaction between bioclastic limestone on the middle gentle slope and micritic limestone on the inner gentle slope are developed in MB1-2 layer with a thickness of about 100m, and the lithology changes frequently. This layer is characterized with shallowing water body, coarsening grains and thickening strata upward, which is recognized as a typical subtidal meter-scale cycle. Based on the Milankovitch cycle principle and the thickness of single layer of 0.1~0.8m, the natural gamma ray log curve is converted to the frequency domain to capture the information of meter-scale cycle by using Matlab software. It is calculated that the cycle period is 2~48 ka, and it is inferred that the interactive sedimentary environment of MB1-2 layer in the study area is controlled by the precession cycle and the obliquity of ecliptic cycle.