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 adopted a combined method of horizontal pipe annular flow experiments and three-dimensional numerical simulations based on the Volume of Fluid (VOF) multiphase flow model. From the perspectives of single-factor analysis and Box-Behnken response surface experimental design, the study systematically investigated the influence laws and multi-factor coupling effects of oil-phase density (880 — 990 kg/m³), water-phase superficial velocity (0.04 — 0.14 m/s), and oil-phase superficial velocity (0.35— 0.95 m/s) on oil transportation efficiency, annular flow stable maintenance length, and oil core eccentricity in a horizontal pipe with an inner diameter of 15 mm. The results show that when the oil-phase density is greater than 950 kg/m³, a stable annular flow structure with an oil core eccentricity of less than 15% and an annular flow stable maintenance length of more than 0.9 m can be achieved by controlling the water-phase superficial velocity within the range of 0.10—0.12 m/s and the oil-phase superficial velocity within 0.6—0.8 m/s. This study provides data and theoretical support for the optimal design of efficient and low-consumption oil-water mixed transportation processes in heavy oil gasification.