In order to improve the atomizing efficiency of ultrasonic spray nozzle, making coaxial jet gasliquid mixing twophase as medium, combining the advantages of effervescent atomization and ultrasonic atomization,a numerical model of the gasliquid two phase flow field in the coaxial type ultrasonic nozzle was established,the internal flow field cloud chart under different gas content and gas phase distribution were researched.The research results indicate that the nozzle flow velocity distribution is layered,there is vortex near the nozzle exit;at the junction of vortex, the fluid velocity reaches maximum;the closer to cavity internal, the smaller the velocity is;the bubble inside the nozzle is a massive distribution, they begin to gather slowly with fluid flowing;considering the fluid turbulence effect in nozzle internal, the gas phase working medium volume is more appropriate within 20%~30%; the more the inlet gas volume fraction is, the larger the gas volume fraction on Y axial direction is;the gas volume fraction on X axial direction is slightly higher than that near the wall of the nozzle,the gas volume fraction is least between the X axis and wall.