The invention discloses a failure protection method for a DC circuit breaker. The method comprises the following steps of carrying out DC line protection action, sending out a DC circuit breaker tripping signal and simultaneously starting circuit breaker failure protection; delaying deltaT1, collecting DC bus voltage Ub and line side voltage U1 and calculating a mean value Ek of difference valuesbetween the DC bus voltage Ub and the line side voltage U1 within deltaT2; judging whether the condition that Ek is greater than Eset is met or not; if so, judging that the circuit breaker is successfully disconnected and returning protection; and if not, judging that the circuit breaker is not successfully disconnected, carrying out circuit breaker failure protection action, sending out a tripping signal to the other circuit breakers connected with a bus and sending out a blocking signal to a local converter. According to the method disclosed by the invention, whether the circuit breaker successfully acts or not can be reliably distinguished only through the bus voltage and the line side voltage of the DC circuit breaker without adopting internal information of the DC circuit breaker.