The invention provides a monitoring device of a nuclear power plant spent fuel pool. The monitoring device comprises a liquid level measuring module and a temperature measuring module and is characterized by further comprising a signal processing cabinet and a power supply cabinet which are electrically connected to the liquid level measuring module and the temperature measuring module respectively, wherein the liquid level measuring module comprises a wave guide head and a wave guide cable; the wave guide head is fixed above the liquid surface of the nuclear power plant spent fuel pool via a mounting bracket; the wave guide cable is electrically connected to the lower part of the wave guide head; a heavy hammer is provided at one downwardly-extended end of the wave guide cable; the temperature measuring module comprises an armored cable fixed on the mounting bracket; the armored cable extends downwardly and is electrically connected to a temperature detector fixed on the heavy hammer; the upper end of the armored cable extends to the distal end and is electrically connected to a temperature transmitter; the signal processing cabinet is arranged out of the nuclear power plant spent fuel pool area and is electrically connected to the wave guide head and the temperature transmitter. Through a measurement manner of remote transmission, the device is capable of obtaining the liquid level and the temperature state in the spent fuel pool, preventing electronic components from being interfered by nuclear radiation and alarming the possible risk in time so as to avoid the potential safety hazard.