The invention relates to a non-full phase protection logic of a circuit breaker. The non-full phase protection logic is characterized by comprising the steps of (1) connecting an auxiliary connection point of a relay at a closing position in a circuit breaker operating box to a switch quantity input terminal of a protection device via a signal power supply of the protection device to be used as opening quantity; (2) judging whether a circuit breaker is closed or not and whether the circuit breaker is in a non-full phase state or not by the protection device according to acquired current quantity of a three-phase circuit breaker and the opening quantity of the auxiliary connection point of the relay at the closing position, and giving out a logic judgment result; and (3) detecting whether the circuit breaker has a zero-sequence current or a negative-sequence current or not according to the acquired current quantity, and performing and logic judgment on the detection result and the non-full phase logic judgment result in the step (2), wherein the judgment result is in a way that the non-full phase circuit breaker is tripped if an output exists. The invention provides the non-full phase protection logic of the circuit breaker comprising the auxiliary connection point of the relay at the closing position of the operating box, and the judgment result is accurate and reliable.