The invention discloses a local relay protection device and method of a circuit breaker configured according to string. The method comprises the following steps of S1, determining whether a substationwiring mode is a complete-string or incomplete-string wiring mode or not, and further determining voltage acquisition quantity of the circuit breaker if the substation wiring mode is the complete-string wiring mode; S2, determining a put-in or exit state of each circuit breaker in a substation; and S3, acquiring corresponding voltage and current analog quantity and switch quantity with regard toeach circuit breaker in the put-in state, independently performing relay protection according to a single-circuit breaker switch, and outputting the switch quantity to the circuit breaker so that a controller trips. By the method, the numbers of local protection devices of the substation can be reduced, connection among the devices is reduced, and a user is convenient to maintain and run.