Abstract: Due to its extremely high heat transfer capability,Microbubble Emission Boiling（MEB）is considered as the ideal means to promote heat exchanger in nuclear power plant.In this paper,the factor triggering MEB was studied by numerical work and boiling instability analysis.A numerical mode with the consideration of Marangoni stress,heat transfer on the vapor-liquid interface and the thermophysical property of test fluids was built based on the visualized study data.The results showed that,the average velocity near the vapor-liquid interface increases while the wall temperature increases.Furthermore,The wall temperature which the average vapor velocity equals to Helmholtz instability limiting speed is consistent with the temperature triggering MEB in the experiment.Thus,Helmholtz instability may be the reason for the collapsing of vapor film when MEB occurs.