Provided are an adaptive control electromagnetic induction energy harvesting method and system for a power transmission line. The method includes acquiring a first electromagnetic induction electromotive force based on an electromagnetic induction energy harvesting device secured to the power transmission line; when the first electromagnetic induction electromotive force is less than an operating electromagnetic induction electromotive force, controlling the electromagnetic induction energy harvesting device to adaptively control a magnetic core unit to perform extension or retraction in a coil unit based on the first electromagnetic induction electromotive force to obtain a second electromagnetic induction electromotive force; performing filtering and rectification processing and voltage conversion processing on at least one of the first electromagnetic induction electromotive force or the second electromagnetic induction electromotive force to obtain an electromagnetic induction output voltage; and performing powering processing or charging processing on an electrical device based on the electromagnetic induction output voltage.