In order to reduce the RE-Fe-B material cost and to balance the utilization of rare earth sources, [(Pr, Nd)_1?xMM_x]_30.3(Fe, Co)_bal- M_0.73B_0.98 (x =0.3, 0.5, 0.7, wt%) magnets were prepared by double main phase (DMP) and single main phase (SMP) processes. DMP magnets are superior to SMP magnets with the same nominal composition in magnetic properties and corrosion resistance. For x=0.5, the magnetic properties of DMP magnets are B_r=1.308 T, H_cj=799.980 kA/m and (BH)_max=325.6436 kJ/m³, which are higher than those for SMP magnets (B_r=1.297 T, H_cj=746.8868 kA/m and (BH)_max=317.8428 kJ/m³) with the same nominal composition, and the impro-ved RE-rich phase distribution and REs heterogeneity distribution are the main reasons. When DMP magnets are exposed to a hygro-thermal environment, there is not only RE-rich phase corrosion, but also pulverized main phase grain due to hydrogenation behavior difference between LaCe-rich and LaCe-lean shell-core within one individual grain. As a result, it is demonstrated that DMP techni-que is an effective approach to improve the permanent magnetic properties and corrosion resistance of MM-based sintered magnets.