CO2 gas phase front migration is an important factor affecting the ultimate recovery and storage efficiency. A quantitative characterization method of CO2 front in multi-layer heterogeneous reservoir was established combining with the X-CT online scan. The migration characteristics and its interlayer differences of the front in multi-layer heterogeneous reservoirs were determined based on the CO2 flooding experiment of three-tube parallel long cores, and the storage efficiency of each core with different permeability was determined simultaneously. The dominant influencing factors of gas phase front migration and rules of each factor were found using numerical simulation of reservoir extraction theoretical model. The results show that the gas front migration in the low permeability reservoir follows the process of “dissolution and diffusion-a retardation-start up”, which decreases slowly at first and then increases rapidly. The migration rate of gas front is positively correlated with permeability, and the migration rate of the front in high permeability core is more than 20% faster than that in low permeability. The stratified storage efficiency was ranked as medium permeability layer > high permeability layer > low permeability layer, and the maximum difference was close to 20%. The main sensitive factors of front migration are permeability, gas injection rate and well spacing. The prediction chart of front migration with the influence of three factors is established. The late front velocity of ultra-low permeability reservoir is 40% lower than that of general low permeability reservoir.