During the thermal recovery of heavy oil, sand is often produced in the formation, and this sand is carried into the surface processing system with high-viscosity heavy oil, which causes serious safety hazards for production facilities and pipelines. Therefore, it is necessary to conduct research on heavy-oil desanding technology to fundamentally eliminate the risks that sand poses to equipment and pipelines. In this study, a heavy-oil desanding experiment was carried out under full consideration of the influence of the water content, temperature and surfactants, and the optimal operating parameter range for achieving a high sand removal rate was identified. The experimental results showed that a high-efficiency desanding effect cannot be achieved by only heating and mixing water and that adding surfactants can significantly improve the efficiency of high-viscosity oil hydrocyclone desanding. To explore the mechanism of surfactant-assisted hydrocyclone desanding, the effect and mechanism of surfactants in promoting high-viscosity oil desanding was analyzed from the perspective of discrete-phase droplet dynamics. The demulsifier promoted the demulsification and stratification of heavy-oil emulsions, the oil droplets formed agglomerates with large particle sizes, and the oil-water phase was rapidly stratified near the vortex finder of the hydrocyclone. Even under a high oil phase viscosity (984 mPa s), the centrifugal field of the hydrocyclone was less affected. At this time, a considerable sand removal rate could be achieved. The viscosity reducer had the same water stratification function as the demulsifier and also promoted the phase inversion of the W/O (water in oil) emulsion to form an O/W(oil in water) emulsion with lower viscosity, significantly reduced the drag force of sand, and greatly improved the sand removal efficiency.