Circuit breaker capable of not interrupting protection during online firmware upgrading

A circuit breaker without interrupting protection during online firmware upgrading comprises an MCU control chip and a storage medium storing a main program and a BootLoader program, the BootLoader program comprises a main program firmware upgrading program and a standby main protection program, an interruption setting step comprises the steps that an alternating current period T is fixedly divided into N equal parts, the timing interruption time is set according to T/N, and the main program firmware upgrading program and the standby main protection program are stored in the main program firmware upgrading program; when the MCU control chip executes the main program firmware upgrading program, the standby main protection program is executed through timing interruption; the main program firmware upgrading program reads firmware upgrading package data and writes the firmware upgrading package data into a storage medium so as to update the main program; the standby main protection program samples and stores a cu