The invention discloses a protection device online monitoring and intelligent diagnosis system. The system comprises protection device state monitoring and diagnosis devices deployed on a substation side and a protection device online monitoring module deployed on a dispatch side master station system. Each protection device state monitoring and diagnosis device on the substation side is composedof a data acquisition unit and a data management unit. Each data acquisition unit acquires the data of a process layer device through a process layer network. Each data management unit acquires data from the data acquisition unit and a station control layer network, carries out analysis and processing, realizes the functions of online monitoring and diagnosis, and uploads diagnostic information toa dispatch master station through DL/T860 or DL/T476. The protection device online monitoring module on a dispatch side displays the communication status of each protection device state monitoring and diagnosis device connected with the module in real time through a graphical interface, and periodically generates the communication state report of all accessed protection device state monitoring and diagnosis devices.