Abstract: In the scientific and engineering practices, such as the aerodynamic loads on near space aircrafts, the orbital transfer and attitude adjustment of spacecrafts, and the mass/heat transfer of micro-scale devices, there are a large amount of multi-regime (multi-scale) flows. The appearance of multi-regimes can be both sequential and spatial, and the latter one is recognized as the complicated local rarefied problem. Since the problem of multi-regime flows is a challenge to the numerical methods, a series of efficient methods which were designed to solve both the continuum flow and rarefied flow in a unified way were proposed in these years, such as the deterministic UGKS, GKUA and DUGKS methods, along with the USP-BGK and UGKWP methods in stochastic particle frameworks. In this paper, the deterministic unified methods and the stochastic unified methods were reviewed and discussed. For each method, the realization of its unified property was discussed along with the theoretical basis. The current advances, potential application value, and extendibility of each method were also discussed in this paper.