Abstract: Magnetic Resonance Velocimetry (MRV) has the unique advantage of rapidly measuring three-dimensional three-component (3D3C) velocity distributions in complex structures, meanwhile it doesn’t need complex optical systems and tracer particles. MRV has become an important means for the study of full flow field. The full-field 3D velocity distribution in a three-pass serpentine channel was measured successfully. Results indicate that MRV has the ability to accurately resolve the complex 3D flow characteristics in the multi-pass channel. From the full-field 3D velocity distribution, it could be found that the flow near the bends has complex 3D features. The secondary flow is obvious on the cross-sections near the bends, which directs from the center of the channel to the upper and lower end walls. Dean vortices were observed in the right-angle bend, U-shaped bend and their downstream clearly. Flow driven by the Dean vortex directs to the upper and lower end walls, which is believed to be the essential reason for local heat transfer enhancement.