The invention discloses a fault diagnosis method and device of a plunger pump, and belongs to the technical field of oil field exploitation. The method comprises the following steps that running parameters of the plunger pump are obtained, wherein the running parameters comprise a plurality of vibration amplitudes, instantaneous flow rates, outlet pressures and electrical parameters; one vibrationamplitude greater than a preset amplitude is selected from the vibration amplitudes; and when at least one vibration amplitude is selected, fault information of the plunger pump is determined based on the at least one vibration amplitude, the instantaneous flow rates, the outlet pressures and the electrical parameters. The vibration amplitudes, the instantaneous flow rates, the outlet pressures and the electrical parameters are obtained in real time, and the plunger pump is subjected to comprehensive fault diagnosis based on the obtained vibration amplitudes, the instantaneous flow rates, theoutlet pressures and the electrical parameters, so that fault reasons and fault positions of the plunger pump can be determined, and accuracy of plunger pump fault diagnosis is improved.