The invention discloses a nuclear power plant reactor pressure vessel irradiation damage monitoring method which comprises the following steps: measuring the initial nano-indentation hardness h0 of a reactor pressure vessel steel monitoring part before the first charging operation of a nuclear power plant; measuring the nano-indentation hardness h of the same monitoring part of the reactor pressure vessel steel at any time point after irradiation damage during normal operation of the nuclear power plant; calculating a nano-indentation hardness change rate delta (h) of the reactor pressure vessel steel in the irradiation damage process based on the initial nano-indentation hardness h0 and the nano-indentation hardness h measured at any time point, and calculating strength parameters of the reactor pressure vessel steel in the irradiation damage process according to the nano-indentation hardness change rate delta (h); and analyzing and evaluating the irradiation damage degree of the reactor pressure vessel steel based on the strength parameters. The monitoring method disclosed by the invention is economic, environment-friendly, safe and efficient, repeated measurement can be realized, and the irradiation damage degrees of multiple positions of the reactor pressure vessel can be simultaneously monitored.