The invention relates to a micro-inductor with a planar core helical structure, and a preparation method thereof, which belong to the microelectronic technical field. The micro-inductor comprises a substrate, a magnetic core material, an insulating material, a coil with a planar helical structure, pins and lead wires, wherein, the coil with the planar helical structure is wrapped by two layers of core material and separated by polyimide; and a central pin is connected with external pins. The process is as follows: sputtering of a layer of Cr, whirl coating, photoetching, developing, etching and overlay alignment symbols making; bonding of the magnetic core material, whirl coating, photoetching, developing, etching of the magnetic core material; fling, drying and solidifying of polyimide, and polishing; sputtering, whirl coating, photoetching, developing, galvanization, and manufacturing of the coil with a planar helical structure, lead wires and pins; fling, drying and solidifying of polyimide, and polishing; sputtering of a layer of Ti, whirl coating, photoetching, developing and etching; and bonding of the magnetic core material, whirl coating, photoetching, developing, and etching of the magnetic core material. The method greatly reduces the high-frequency loss of the micro-inductor and effectively improves the high-frequency property thereof.