The present invention provides a direct current system and a failure protection method of a breaker in a starting process thereof. The method comprises the steps of: in a direct system starting process, controlling starting resistance work in a starting loop, when it is detected that a valve side of a converter valve generates earth faults, disconnecting a breaker at the network side of the converter valve; and detecting a current value of the network side of the converter valve, and if the current value of the network side of the converter valve is larger than a set value and there are failure open-in signals, determining that the breaker is failed in motion. According to the technical scheme provided by the invention, when the failure protection of the breaker at the network side is determined, the current value of the circuit connected with the converter valve at the network side is taken as current criterion so as to solve the problem that the breaker is failed in protection and cannot perform motion caused by large current transformer change and poor precision when the small current value is collected when a current value on a lead string is taken as the current criterion.