This study explored the design of a novel auto-gaping magnetic pole system for finishing the inner surface of non-circular pipes using a magnetic abrasive finishing (MAF) process. Non-circular pipes are widely used for the transportation of ultra-high purity substances, including gases and fluids in many industries for semiconductor, medical, and aerospace applications. MAF process typically utilizes non-movable magnetic poles. However, due to the noncircular cross-section of the pipe, the magnetic flux density, produced by non-movable magnetic poles, across the polishing surface will exhibit huge variations, resulting in uneven and poor finish at some areas. The proposed auto-gaping magnetic pole system allows the magnetic poles to move so that they can track the workpiece surface to keep the gap between the magnetic pole and workpiece’s external surface constant. As a result, the magnetic densities can be maintained at desired values to achieve even and effective finishing by MAF process. Elliptical pipes were used as the non-circular pipes for experimental validation under different MAF process parameters. The results showed that this novel technique for inner surface finishing of a non-circular pipe is capable of improving the surface roughness, reducing the Ra values from over 0.20 μm to 0.05 μm or lower, across the entire inner surface of the elliptical pipe. In addition, superior material removal efficiency was achieved. The results demonstrate that the MAF process combined with a novel auto-gaping magnetic pole system is feasible to produce the ultra-smooth inner surface of non-circular pipe.