The formation of large- scale burial dolomite, especially the migration mechanism of magnesium- enriched fluid, has always been the focus of debate among geologists in the genesis of dolomite. Considering the burial dolomite of Penglaiba Formation in Tarim basin, the formation mechanism of massive burial dolomite was studied by integrating magnesium isotope and petrology, conventional geochemical analysis of carbon and oxygen isotopes, strontium isotopes and strontium content. The analysis shows that although the magnesium isotope distribution of different types of dolomites in the Penglaiba Formation overlaps, the difference is obvious. The microbial dolomites have the magnesium isotope value of 2. 34‰~2. 02‰ while those of fine to medium crystalline dolomite range from 2. 24‰ to 1. 66‰, with an average of 2. 04‰. The magnesium isotopes of coarse crystalline dolomite are concentrated in 2. 24‰~1. 89‰ range, with an average value of 2. 21‰. In contrast, the magnesium isotope of limestone of the Penglaiba Formation ranges between 3. 63‰ to 2. 82‰, which is obviously more negative than that of dolomite. The compositions of magnesium isotope, oxygen isotope, and strontium isotope and strontium contents show regular cyclic changes in high- frequency cycles, corresponding to three processes of dolomitization: upward lightening- reflux superimposed by burial dolomitization, upward weighting- Sabkha superimposed by burial dolomitization, and upward weighting- burial dolomitization. Furthermore, according to the lateral variation of dolomite crystal and strontium content within cycles, the response principle of dolomite crystal in the process of lateral migration of buried dolomitizing fluid is clarified. It is recognized that the massive dolomite is formed by the superposition of multi- stage dolomitization. There are both intralayer dolomitized fluids and exotic dolomitized fluids. It is jointly controlled by sedimentary facies and tectonic burial evolution history. A large number of stacking penecontemporaneous dolomites formed under sea level fluctuations constituting the basis of the large- scale massive burial dolomite, especially the permeable reflux dolomite with considerable primary pores. The higher the proportion of penecontemporaneous dolomite in the high- frequency sequence framework, the more conducive it is to the infiltration and diffusion of dolomitizing fluids under burial conditions, so as to increase the proportion of dolomite and constitute large- scale massive burial dolomite.