Abstract: In order to quantitatively analyze the error of CCMS (core cooling monitoring system) vessel water level measurement induced by the variation of the characteristic of the primary pumps and correlative parameters (power grid frequency, void fraction etc.) in CPR1000 nuclear power plant, and then evaluate its impact on accident management process, based on the principle of CCMS vessel water level measurement, the formulae to calculate the error through the parameters of the primary pumps were proposed, and the quantitative analysis by using this calculations was made in the paper. The results show that the error induced by the parameter variation can be ignored, except the under-estimated error induced by function degradation of the primary pump. After the impact of the under-estimated error on the operator’s critical safety actions in the view of SOP (state oriented procedure) was analyzed, the conclusion is made that the error may disturb the operations relative to primary pumps, but will not obstruct the critical safety actions to be implemented in SOP.