A processor duplexing method is applied to a 3G mobile communication system switching operation without involving application software. In this method, Real-Time operating system (RTOS) detects that a duplexing operation is being performed. While the duplexing switching operation is being performed, the RTOS and a PCI controlling unit dump a memory of an active board to a standby board, thereby synchronizing a memory between the active board and the standby board. Once the duplexing switching operation is complete, the standby board sequentially starts operation of the active board. In this method, duplexing of a processor level is performed without using application software in the RTOS. Instead, duplexing is a performed by a substructure (hardware and OS). As a result the burden of having the application software grow larger and more complicated is significantly reduced.