Using Al powder as diffused source, the influence of grain boundary diffused processes on the microstructure and magnetic properties were investigated. It is found that the optimum magnetic properties including the coercivity of 1131 kA/m and the maximum energy product of 252 kJ/m3 can be achieved, increasing by 16% and 9.6%, respectively, meanwhile, the temperature stability is also improved. Microstructural investigation reveals that Al is mainly distributed in the intergranular RE-rich phase, and the morphology of RE-rich phase changes from large block to thin layer. Smoother and more straight interface can be obtained, which can restrain the nucleation of anti-magnetization domain, reducing the demagnetization field. In addition, the Al in the intergranular phase is beneficial in elevating the corrosion potential, and the decreased corrosion current density should be attributed to the changes of RE-rich phase distribution.