Heavy oil reserves play an important role in world's energy supply. Steam injection is among the most widely used thermal recovery methods for heavy oil recovery. However, the disadvantages such as low oil recovery, high energy consumption and large greenhouse gas emissions, etc. limited the application of this technology. The hybrid injection of steam and air is considered as an effective alternative for pure steam injection. In this paper, a two-dimensional visualized model filled with glass beads was introduced to quantitatively investigate the sweep efficiency and steam channeling of steam and steam/air injection for a typical heavy oil from a macroscopic perspective. On the basis of the experiments, pore-scale analysis was performed to study the enhanced oil recovery mechanisms of steam/air injection. The experimental results indicated that the injected continuous air was cut off into small gas bubbles to form Jamin effect in porous media, along with the react between air and heavy oil to increase the macroscopic sweep efficiency and microscopic oil displacement efficiency. The sweep efficiency and oil recovery of steam/air injection was 90.22% and 61.87%, respectively, which were 22.26% and 10.67% higher than those of pure steam injection.