In order to reduce the RE-Fe-B material cost and balance the utilization of rare earth sources, [(Pr,Nd)1-xMMx]30.3(Fe,Co)balM0.73B0.98 ( x = 0.3, 0.5 and 0.7 ) were prepared by double main phase(DMP) and single main phase process(SMP) respectively. DMP magnets exhibit superior magnetic properties and corrosion resistance to SMP magnets with same nominal composition. For x = 0.5 DMP magnets, the magnetic properties remain in Br = 13.08 kGs, Hcj = 10.05 kOe, and (BH)max = 40.91 MGOe. These properties are higher than that for SMP magnets (Br = 12.97 kGs, Hcj = 9.383 kOe, and (BH)max = 39.93 MGOe) with the same nominal composition. The enhanced RE-rich phase distribution and REs heterogeneity distribution are the main origin. When DMP magnets are exposed in hygrothermal environment, there are not only RE-rich phase corroded, but also there exist main phase grain pulverized due to hydrogenation behavior difference from LaCe-rich and LaCe-lean shell-core within one individual grain. As a result, it is demonstrated that double main phase technology is an effective approach to improve the permanent magnetic properties and corrosion resistance of MM based sintered magnets..