The invention provides a preparation method of an amorphous or nanocrystalline soft magnetic powder core. The method includes the following steps that (1) amorphous or nanocrystalline soft magnetic powder is subjected to passivating treatment; (2) passivated amorphous or nanocrystalline soft magnetic powder is subjected to cladding treatment by means of an organic binding agent; (3) then a lubricating agent and an insulating agent is added into magnetic powder obtained in the step (2) to obtain to-be-compressed magnetic powder; (4) the obtained to-be-compressed magnetic powder is subjected to pressing forming at the normal temperature through a mold, and a compressed blank is obtained after demolding is finished; (5) pressure stress is exerted on the obtained compressed blank for solidification or plastification; (6) a compressed blank obtained in the step (5) is impregnated in an inorganic binding agent solution and stabilizing treatment is performed; (7) a compressed blank obtained in the step (6) is subjected to high-temperature annealing heat treatment; (8) an annealed compressed blank framework obtained in the step (7) is impregnated in a high-strength binding agent solution and solidification or stabilizing treatment is performed; and (9) a high-strength blank obtained in the step (8) is subjected to subsequent processing to obtain a finished product. By means of the technical scheme, the amorphous or nanocrystalline soft magnetic powder core with high density and high soft magnetic property can be obtained with low forming pressure.