Abstract: In order to solve the problem of oil-water mixing transport in heavy oil gasification process by using annular flow transport technology, this study adopts a combination of horizontal pipeline annular flow experiments and three-dimensional numerical simulation based on the VOF multiphase flow model, and systematically investigates the effects of oil-phase density (880 ~ 990 kg/m³), water-phase apparent flow rate (0.04 ~ 0.14 m/s), and oil-phase apparent flow rate (0.35 ~ 0.95 m/s) on oil transport efficiency, annular flow stability maintenance length, and oil-phase stability maintenance length within 15 mm inner diameter horizontal pipeline. The results show that when the density of the oil phase is greater than 950 kg/m³, and the apparent flow rate of the water phase is controlled in the range of 0.10 ~ 0.12 m/s, and the apparent flow rate of the oil phase is controlled in the range of 0.6 ~ 0.8 m/s, a stable annular flow structure with a core eccentricity of less than 15% and an annular flow stability maintenance length of more than 0.9 m can be realized. This study provides a theoretical basis for the optimal design of the high-efficiency and low-consumption oil-water mixing and conveying process for heavy oil gasification.