Experiments were conducted to investigate forced flow boiling heat transfer of non-azeotropic refrigerant mixtures of R32 and R134a in a horizontal mini-scale tube.The dependence of heat transfer coefficient on mass quality，heat flux and mass flux was analyzed and the heat transfer mechanism under each working condition was discussed.The forced flow boiling heat transfer in the mini-scale tube and large-scale tube was compared and discussed.The results showed that mass quality and mass flux had nearly no effect on forced flow boiling heat transfer，but heat flux affected heat transfer greatly and nucleation boiling heat transfer played an important role in most of the mass quality range.Only when heat flux was very low，mass flux and mass quality had some effect on forced flow boiling heat transfer and forced convective heat transfer dominated.Compared with the large-scale tube，fully suppressed nucleate boiling was not observed and heat transfer mechanism was dominated by nucleation boiling in the mini-scale tube due to size effect.