A failure downgrade operation method for a nuclear power plant control room, the method comprising: S11: using a plant computer information and control system, referred to as a KIC system to construct a pre-defense line in a control room defense in depth system, wherein in normal conditions, all Human-System Interfaces, HSIs functions are available, a plurality of digital work places configured by the KIC system monitor the nuclear power plant; when the KIC system equipment fails, the KIC system redistributes safety monitoring work to the work places, and the KIC system operates in downgrade mode or even fails; S12: using an an Auxiliary Control Panel, ACP and an Emergency Control Panel, ECP to construct a main defense line in the control room defense in depth system, wherein the ACP is configured to replace the KIC system to take over control authority of the nuclear power plant and perform safety monitoring of the nuclear power plant when the KIC system fails; S13: using a Serious Accident Panel, SAP panel to construct a diversity defense line in the control room defense in depth system, wherein the SAP panel is configured to independently monitor the nuclear power plant when the Digital Control System, DCS protection system of the nuclear power plant fails due to a digital common mode failure; and S14: using an SAP panel to construct a serious accident mitigation line in the control room defense in depth system, wherein the SAP panel is configured to provide operators with relevant serious accident prevention and mitigation means when a serious accident occurs in the nuclear power plant and other safety monitoring methods fail. S11: using a plant computer information and control system, referred to as a KIC system to construct a pre-defense line in a control room defense in depth system, wherein in normal conditions, all Human-System Interfaces, HSIs functions are available, a plurality of digital work places configured by the KIC system monitor the nuclear power plant; when the KIC system equipment fails, the KIC system redistributes safety monitoring work to the work places, and the KIC system operates in downgrade mode or even fails; S12: using an an Auxiliary Control Panel, ACP and an Emergency Control Panel, ECP to construct a main defense line in the control room defense in depth system, wherein the ACP is configured to replace the KIC system to take over control authority of the nuclear power plant and perform safety monitoring of the nuclear power plant when the KIC system fails; S13: using a Serious Accident Panel, SAP panel to construct a diversity defense line in the control room defense in depth system, wherein the SAP panel is configured to independently monitor the nuclear power plant when the Digital Control System, DCS protection system of the nuclear power plant fails due to a digital common mode failure; and S14: using an SAP panel to construct a serious accident mitigation line in the control room defense in depth system, wherein the SAP panel is configured to provide operators with relevant serious accident prevention and mitigation means when a serious accident occurs in the nuclear power plant and other safety monitoring methods fail.