Abstract: Experimental study was reported for flow boiling heat transfer of a nonazeotropic mixture of R32/R134a［25%(mass)/75%(mass)］inside both smooth and microfin tubes with internal spiral grooves.The influences of mass quality，heat flux & mass flow rate on A_f(heat transfer enhanced coefficient)are discussed, respectively.The experimental results show that the microfin tubes have distinct performance advantages over the smooth tube at similar conditions,the varying of heat flux has the greatest effect on A_f,and A_f varied from 1.4—2.2.