Aiming at the problems such as weak system processing capability and insufficient stability in online monitoring of circuit breakers, the ARM, DSP and FPGA three-core platform are used to realize the on-line monitoring of the circuit breaker. The on-line monitoring function of circuit breaker is divided into 3 parts: data acquisition, data operation and human-computer interaction. Data acquisition is completed by FPGA control ADS8568. The circuit breaker state variables are passed into the system by sensors. The DSP performs wavelet decomposition five times on the signal collected by FPGA using db2 wavelet. Processed data is transmitted to the ARM through the dual-core communication mechanism based on Syslink heterogeneous, and finally the human-computer interaction is completed by the ARM. The scheme gives full play to the advantages of three control cores, so that it has better data processing ability. Through testing, the on-line monitoring system of circuit breaker based on three-core structure has a better performance than the original system.