Keeping the heat flux density and the temperature of water at inlet constant, cooling experiments on non-boiling heat transfer with air-assist atomization are carried out. The influences of liquid mass flow rate and pressure, air to liquid ratio and nitrogen pressure on sauter diameter dSMD are analyzed. The heat transfer capacity and temperature uniformity are further studied respectively. The results show that when the air-liquid mass flow ratio is above 5%, the same nitrogen and liquid pressure can get a better heat transfer due to optimal match of gas-liquid relative velocity, the nitrogen kinetic energy utilization and gas consumption rate, and as the liquid pressure is slightly lower than the nitrogen pressure uniform temperature distribution can be achieved. When the air-liquid mass flow ratio is below 5%, a better heat transfer and temperature distribution can be gotten under the condition of the nitrogen pressure slightly higher than the liquid pressure, which ensure the utilization of gas kinetic energy while increase the relative velocity and optimize the droplet atomization and distribution.