The invention discloses a comprehensive detection device of a direct-current transmission valve cooling system instrument. The comprehensive detection device comprises a temperature instrument detection unit, a pressure instrument detection unit, a liquid level instrument detection unit, a conductivity instrument detection unit and a flow instrument detection unit and further comprises a programmable logic controller (PLC) control system and an upper computer. The temperature instrument detection unit, the pressure instrument detection unit, the liquid level instrument detection unit, the conductivity instrument detection unit and the flow instrument detection unit are communicated with the PLC control system, and the upper computer is connected with the control system through optical fibers. The comprehensive detection device can conduct comprehensive detection analysis on accuracy of various direct-current transmission valve cooling system instruments, improves system management level of valve cooling equipment, strengthens risk pre-control capability, develops detection analysis work, and simultaneously provides scientific data basis for building equipment archives for on-line monitoring instruments of a valve cooling system, formulating test standards and the like.