In order to better understand reservoir characteristics of Iraq Missan Oilfield, we study Mishrif group carbonate reservoir characteristics, diagenesis and reservoir main controlling factors. Through the analysis of core, rock slice, casting slice and experiment data, study the reservoir characteristics such as the lithology characteristics, reservoir space types, sedimentary phase characteristics and physical characteristics and so on, diagenesis and reservoir controlling factors. The results show that the reservoir space is mainly dissolved pore, reservoir physical property is medium porosity and low permeability. And the Mishrif group obtain a variety of diagenesis, including compaction, denudation, packing action, cementation, dolomitization, rejuvenation of crystals, biological mud crystallization. Main controlling factors of reservoir as follows: depositional environment control the development of primary pore which consists of organic framework pore, intergranular pore and so on. Early cementation led to reservoir quality damage and dissolution improved reservoir property and fractures caused by tectonic movement not only generate dissolution pore but also can be turn into migration pathway.