The invention discloses a monitoring method for radiation embrittlement of a reactor pressure vessel of a nuclear power plant. The monitoring method comprises the following steps: 1) acquiring an electromagnetic property parameter value X0 and a mechanical property parameter value Y0 of reactor pressure vessel steel at an initial state; 2) performing on-time testing on an electromagnetic propertyparameter X of a monitoring part of the reactor pressure vessel steel at one specific time point after radiation embrittlement; and 3) according to a function relation expression delta (Y)=A+B*exp[C*delta(X)], confirming a mechanical property parameter Y, wherein the electromagnetic property change rate delta (X)=IX-X0I/X0; the mechanical property change rate delta (Y)=IY-Y0I/Y0; and A, B and C are calculation coefficients. Compared with the prior art, the monitoring method for radiation embrittlement of the reactor pressure vessel of the nuclear power plant, which is disclosed by the invention, is not only capable of achieving real-time multi-time nondestructive measurement, but also precise in data, good in testing operation security, and capable of monitoring radiation embrittlement degrees of multiple positions of the reactor pressure vessel simultaneously.