A type of sintered Nd—Fe—B permanent magnet with high intrinsic coercivity of about 30KOe or more is produced by dual alloy method. The method comprises the following steps: preparing the powders of master phase alloy and intergranular phase alloy respectively, mixing the powders, compacting the powders in magnetic field, sintering the compacted body at 1050˜1125° C. and annealing at 890-1000° C. and 500-650° C. successively. In the process of preparing the powder of intergranular phase alloy, the nano-powder additive selected from the group consisting of NiAl, TiC, SiC, AlN, TiN, ZrN and the combination thereof is used to modify the powder of intergranular phase alloy.