This paper proposed an alternating elliptical U-bend cooling channel, which can be applied in the midchord region of gas turbine blade and manufactured by precision casting, based on the optimal flow field structure deduced from the field synergy principle, and investigated the flow and heat transfer characteristics in this alternating elliptical U-bend cooling channel thoroughly. Numerical simulations were performed by using three-dimensional steady solver of Reynolds-averaged Navier–Stokes equations with the standard k–ε turbulence model. The influence of alternating of cross section on heat transfer and pressure drop of the channel was studied by comparing with the smooth elliptical U-bend channel. On this basis, the effect of aspect ratio (length ratio of the major axis to the minor axis) and alternating angle were further investigated. The results showed that, in the first pass of the alternating elliptical U-bend channel, for different Re, four or eight longitudinal vortices were generated. In the second pass, the alternating elliptical channel restrained the flow separation to a certain extent and a double-vortex structure was formed. The averaged Nusselt number of the alternating elliptical U-bend channel was significantly higher than that of the smooth channel, but the pressure loss only increased slightly. With the increase of aspect ratio, the thermal performance of the channel increased, and when the alternating angle is between 40 deg and 90 deg, the thermal performance nearly kept constant and also the best.