Abstract: In order to improve the heat dissipation of electronic devices,reduce the problem of lower devices performance and short working life which was caused by high temperature, the friction and heat transfer characteristics of single phase forced convection in developing region with high heat flux through a multiport microchannel flat tube (MMFT) were comparatively investigated by experiments. Furthermore the influence of heat transfer capability in MMFT with developing flow was evaluated by three aspects: single/double-side heating, different methods of eliminating thermal resistance and different heat flux. The hydraulic diameter of the tube was 1.09mm, aspect ratio was 0.85 and Reynolds number was in the range of 206~4553. The results indicate that friction factor obtained by experiment is in good agreement with the classical developing channel laminar flow theory. In addition to heat transfer, single-side heating is superior to double-side heating whereas the discrepancy reduces with the increase of Reynold number. Different thermal resistance has obvious effect on heat transfer. Brazing lowers the surface temperature of heating device 10℃ than thermally conductive silicone grease. When Re<1000, temperature dependent viscosity variation on the convective heat transfer are significant, however for high Reynold, various heat flux effects Nusselt number little.