The invention provides an on-line measuring method of a circuit breaker, which comprises the following steps: target equipment data is monitored in an on-line manner in real time, wherein the target equipment data comprises mechanical characteristics of the circuit breaker, electrical characteristics of the circuit breaker, the insulation condition of the circuit breaker, the integrity of secondary circuits, the temperature of hydraulic oil, the pressure and an oil pump; an on-line monitoring model file of the circuit breaker is created according to parameter information, a parameter data name, CDC types and postil description; and the model file and the on-line monitoring data are firstly uploaded to a comprehensive treatment unit and then uploaded to a remote monitoring center. The invention further provides an on-line monitoring device of the circuit breaker, so that the work efficiency and the safety of the circuit breaker can be improved.