Numerical simulation of three-dimensional turbulent flow and heat transfer was performed in a multi-pass rectangular (AR = 2:1) rotating cooling channel with and without turning vane in the hub region under various flow conditions, with two different Reynolds numbers of 10000 and 25000, two different channel orientations of 45-deg and 90-deg., and the rotation number varies from 0 to 0.2. The present study provides detailed explanation on the dramatic flow change due to the turning vane. The numerical results show that the addition of vane in hub portion does not cause much impact to the flow before the turn. However, it greatly affects flow behaviors and heat transfer characteristics in the turning region and the third passage after the hub turn. Compared to the cases without turning vane, the vane clearly changes local flow pattern, divides the main flow into two separate streams, and alters the flow reattachment location and vortex distribution. The local heat transfer is influenced by this complex flow field and its effects last from the turn portion to the third passage.