Abstract: An visualization experiment was conducted to study the steam-water two-phase flow phenomena in a saturated porous structure with internal heat source. The porous structure was formed by stacking uniform spheres. The two-phase flow phenomena in porous media were obtained by high-speed camera system and the flow regimes was identified. The influence of pressure and inlet subcooling on the flow regimes was also investigated. The results of visualization experiment show that the flow regimes in porous channel are bubbly flow, bubbly-slug mixed flow, slug flow, slug-annular mixed flow and annular flow. The results also show that the bubbly to transitional flow transition and the transitional to annual flow transition appear at lower superficial steam velocity in the channel with the lower inlet subcooling. The present study also show that the bubbly to transitional flow transition and the transitional to annual flow transition appear at lower superficial steam velocity in the channel with the higher pressure.