Abstract: This paper comprehensively analyzes the impact on the nuclear power plant security when LCA / LCB loses the power. When LCA loses the power, the normal boronization of the reactor coolant is unavailable, only the direct boronization can be used; the normal discharge, excess discharge and low pressure discharge of the pressurizer are unavailable; the reactor trip breakers disconnect and P4 signal appears; the reactor trips or safety injection probably happens for the excessive cooling reactor coolant or too low pressure. When LCB loses the power, normal boronization is available, and normal discharge can be used by manual operation, and the reactor shutdown or safety injection probably also happen for the same reason.