Pressure drop and heat transfer for flow-boiling of water in small-diameter tubes under atmospheric pressure were discussed. The results of experiments were compared with those of several existing correlations and models. The experiments were carried out using atmospheric-pressure water in tubes with inner diameter D ranging from 2.0 to 6.0mm, heated length L from 4.0 to 680.0mm, inlet water subcooling ΔT_in from 70 to 90K, and mass velocity G from 100 to 10170kg/ (m²·s). The highest heat flux q attained was 33MW/m². Interesting phenomena were observed in small-diameter tubes with a very long or very short heated length. The most suitable correlations for predicting the pressure drop and heat transfer in small-diameter tubes were discussed.