Small channel heat transfer with condensation or boiling is utilized to handle the more and more intense heat dissipation load nowadays. To further enhance the annular condensation heat transfer inside these channels, diverging-shaped small channel is considered in this work analytically. It is testified that diverging channels do improve condensation heat transfer significantly compared to small channels with constant cross-sectional area. With refrigerant mass flux density increasing or channel size decreasing, diverging channels become more and more efficient in enhancing condensation heat transfer. (C) 2018 Elsevier Ltd. All rights reserved.