The bubble generation performance and liquid volumetric mass transfer coefficient kLa of the venturi microbubble generator and the swirl-venturi microbubble generator were evaluated through the high-speed photography and measurement of dissolved oxygen concentration. The results show that the swirl-venturi microbubble generator generates more bubbles with smaller Sauter mean diameter than the venturi microbubble generator. And the maximum stable bubble size of the swirl-venturi microbubble generator is also smaller than that of the venturi microbubble generator. Moreover, the maximum stable bubble size of the swirl-venturi microbubble generator is not sensitive to the increase of superficial gas velocity, which indicates that the swirl-venturi microbubble generator has a higher probability of breaking bubbles. Eventually, the liquid volumetric mass transfer coefficient kLa of swirl-venturi microbubble generator is measured and higher than that of the venturi microbubble generator at high superficial gas velocity. Based on all above, it can be concluded that the swirl-venturi microbubble generator is a more effective way to generate microbubbles.