The characteristics of heat transfer for CO2 flow boiling in horizontal micro-tube were studied. Experimental conditions:saturated temperature -40-0℃

heat flux 5-35 kW·m-2

mass flow rate 200-1500 kg·m-2·s-1

and inner diameter 1.5 mm. Experimental results show that:the increase of heat flux has significant effect on enhancing nucleate boiling heat transfer

meanwhile speeds up the dryout process and decreases the starting vapor quality of dryout; the effect of mass flow rate on heat transfer coefficient is slight

but as mass flow rate increasing

the starting vapor quality of dryout decreases

and the heat transfer coefficient increases after the dryout happens; the effect of saturation temperature on the physical properties of CO2 is the main cause of the different heat transfer characteristics in different experimental conditions.With the increasing of saturation temperature

the starting vapor quality of dryout has a decline tendency and the heat transfer coefficient has a steeper fall after dryout happens. Compared with the prediction model

the Cheng's model has a higher prediction accuracy

it is presented with 77.1% of predicted points within ±30% and 20.5% mean absolute deviation before dryout phenomenon happened

while it has only 22.9% and 57.8% after dryout phenomenon happened.