The invention relates to a soft magnetic core used for a high-power inverter power supply, and a manufacturing method thereof. The magnetic core is made of an Fe-based amorphous nano-crystalline belt material through winding , and comprises components according to weight percentages as follows: 81%-85% of Fe, 0.01%-5% of Co, 7%-9% of Si, 1.5%-2.5% of B, 1%-2% of Cu, 4%-7% of M, and 0.001%-0.04% of M', wherein M is one or more of Nb, Mo, V, W and Ta, and M' is at least one of Al and Ti. The magnetic core is subjected to anneal in a protective atmosphere or a vacuum; when in anneal, the position of the magnetic core in a furnace is movable or rotatable, a holding temperature is 520-600 DEG C, the holding time is 1-2 hours, and a temperature rise speed is 100 DEG C per hour. The magnetic core manufactured by adopting the method has lower loss, better manufacturing technique properties, and good soft magnetic characteristics; moreover, the downstream processing after the heat treatment is applicable to various technique methods.