This paper refers to the data records of X-ray diffraction, fluid inclusion analysis, thin section analysis, to discuss the factors of the order degree of dolomite of Ordovician Majiagou Group. The research indicates, the dolomitization more thorough, the order degree of dolomite better; as the crystal shape better and crystal size increase, the order degree of dolomite is better than muddy-limestone. CaCO3 mole fraction is more near ideal mole fraction, the order degree is higher. As the increase of Fe2+, Mn2+, the order degree of dolomite decreases. The order degree of dolomite formed in higher temperature is better than that in the lower temperature.