The invention relates to a transformer station grounding network fault diagnosis method based on synthesis of surface potential and magnetic induction strength, which comprises the steps of: a first step, calculating the theoretical surface potential and the magnetic induction strength of a transformer station grounding network; a second step, respectively measuring the surface potential and an induction voltage along a path above a grounding conductor, and furthermore calculating the magnetic induction strength according to the induction voltage; a third step, according to the surface potential of a measuring point and a measured value of the magnetic induction strength, respectively calculating the surface potential and the magnetic induction strength of each conductor according to a robustness least square method for acquiring the surface potential and the magnetic induction strength of the grounding network conductor; and a fourth step, comparing the surface potential and the magnetic induction strength of an actual grounding network with the surface potential and the magnetic induction strength which are theoretically calculated in a normal working state, and calculating a comprehensive grey absolute correlation degree ADI. Compared with the prior art, the transformer station grounding network fault diagnosis method has advantages of improving operation reliability of the transformer station grounding network, etc.