Rare earth auxiliary alloy powder and preparation method and application thereof

The rare earth auxiliary alloy powder is prepared according to the weight percentage of RExM100-x-yBy, RE is one or a mixture of more than one of Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu, M is one or a mixture of more than one of Mg, Al, Ca, Ti, V, Fe, Co, Ni, Cu, Zn, Ga, In, Sn, Sb and Bi, x is larger than or equal to 30% and smaller than or equal to 80%, and y is larger than or equal to 0 and smaller than or equal to 0.5%. RE is proportionally added in the form of a metal simple substance or RE-Fe, M is proportionally added in the form of powder or alloy powder, B is proportionally added in the form of B-Fe sand, the mixture is added into a hydrogen decrepitation furnace for mixed hydrogen decrepitation, and the rare earth auxiliary alloy powder is prepared. When the method is applied to preparation of the sintered neodymium-iron-boron magnet, the coercive force improvement amplitude can be improved, the residual magnetism reduction amplitude is reduced, and the use amount of heavy r