The work aims to improve the inner surface quality of H63 brass bend pipe, shorten its processing period and improve its service life. A six-degree-of-freedom manipulator was used to drive the magnetic field generator to drive the auxiliary magnet in bending pipe to conduct grinding test. The spherical magnet and spherical with ring grooves magnet were used as auxiliary magnet for grinding, and the Ansoft software was used to analyze the changes of magnetic lines and magnetic induction intensity in the processing area after two different kinds of auxiliary magnets were added. The principle and grinding track of two different kinds of auxiliary magnets for grinding the inner surface of bending pipe were explored. Two different kinds of auxiliary magnets of grinding test data were compared and analyzed with the stylus surface roughness meter and the ultra depth 3D microscope. When the spherical magnet were used as auxiliary magnet, the grinding time was 60 minutes, the inner surface roughness of H63 brass bend pipe was reduced from Ra=0.833 μm to Ra=0.238 μm; after continuing grinding for 15 minutes, the surface roughness was reduced from Ra=0.238 μm to Ra=0.194 μm. When the spherical with ring grooves magnet were used as auxiliary magnet, the grinding time was 60 minutes, the inner surface roughness of H63 brass bend pipe was reduced from Ra=0.834 μm to Ra=0.172 μm; after continuing grinding for 15 minutes, the surface roughness was changed from Ra=0.172 μm to Ra=0.176 μm. When the spherical with ring grooves magnet was used as auxiliary magnet, the grinding efficiency was increased by 20%. When the spherical with ring grooves magnet was used as auxiliary magnet, the grinding track of the inner surface of bending pipe is dense homogeneous double helix curve; it can avoid the sharp point effect caused by the grinding of spherical auxiliary magnet. At the same time, it promotes the rolling and updating of magnetic abrasive particles, and then delays blade passivation and shorten the grinding time; it solves the problem of original inner surface quality defect of bend pipe.