Flow boiling characteristics of nonazeotropic mixture of R32/R134a inside microfin tubes were investigated experimentally to obtain the effects of fin height and fin number on heat transfer characteristics of nonazeotropic mixture. Heat transfer performances of three microfin tubes with different geometry parameters were analyzed comprehensively. At thesame time, the comparisons between the coefficients of microfin tubes and smooth tube were made. Among the three kinds of microfin tubes, the microfin tube, whose fin height is 0.2 mm, and fin nomber is 60,is found harvning the optimal heat transfer characteristics. Hearvt trensfer performances of microfin tubes are better than that of smoth tube obviously.