The invention provides an online monitoring device and an online monitoring method for intelligent electronic devices. The online monitoring device comprises an Ethernet controller, an FPGA (field programmable gate array) controller, an output module, a switching input module, an RS485 communication module and a power module, wherein the switching input module is in one-way connection with the FPGA controller, the Ethernet controller and the RS485 communication module are in double-way connection with the FPGA controller, and the FPGA controller is in one-way connection with the output module. The online monitoring device achieves analog simulation of operating environments of intelligent circuit breaker primary devices and is powerful in interaction function, convenient to operate and universal in interface. The online monitoring method has the advantages that experimental costs are reduced while experimental period is shortened; the online monitoring method is high in system expandability, thereby being applicable to performance monitoring of current rapid intelligent electronics development technology.