The invention discloses a bolt-based diagnosing method of hydro-generator rotor winding inter-turn short circuit. The method is characterized in that one section of the bolt of a hydro-generator stator core is selected, measuring lines are guided out at two ends of the bolt section through gaps among stator core sections, the measuring lines are connected with a data collecting device, and the induction voltage of the bolt is collected in real time by an online collecting system; real-time data processing is performed on the collected bolt induction voltage, the induction voltage deviation of the bolt is compared when the same position of different magnetic poles sweeps over the bolt, and the fact that the hydro-generator rotor winding inter-turn short circuit occurs when the voltage deviation exceeds a set threshold. By the method, the defects in the prior art can be overcome, and the diagnosing level of similar faults can be increased.