The invention discloses a system and a method for corrosion diagnosis of a grounding grid of a transformer substation on the basis of an inductive apparent magnetic impedance method. The system includes a transmitter that is connected between two down-lead conductors of the grounding grid of the transformer substation. The transmitter employs a sine excitation source and is used for injecting a frequency-adjustable excitation current into the grounding grid so as to excite a magnetic induction intensity signal of ground surface; the system also includes: a trolley arranged on the ground, on which two detection coils are arranged vertically to each other and are used for detecting the magnetic induction intensity signal and converts the magnetic induction intensity signal into an inductionvoltage signal; the detection coils are successively connected to a receiver and an upper computer, wherein the receiver is used for collecting and processing the induction voltage signal so as to acquire amplitude spectrum and phase spectrum, and the upper computer draws two-dimensional and three-dimensional figures of the amplitude and phase by means of Lab VIEW software. In the invention, by means of injection of the frequency-adjustable large excitation current and measurement of trapped wave circuits and wave filtering on hardware, the system can avoid intensive electromagnetic interference from the transformer substation and can provide more reliable measurement data.