The utility model discloses an energy transition and signal processing circuit of series compensation protection system secondary sampling device, which comprises an electric power and communication control signal separation circuit, a DC-DC converter circuit, a clock signal extraction circuit and a low-voltage signal discrimination circuit. An optical current transducer converts a laser signal into electric energy to output to the electric power and communication control signal separation circuit, the electric power and communication control signal separation circuit outputs three paths for separate processing, one path outputs the electric energy to the DC-DC conversion circuit, one path outputs the communication control signal to the clock signal extraction circuit, and one path outputs the low-voltage signal to the low-voltage signal discrimination circuit. The electric energy is adjusted, filtered and denoised by using the DC-DC converter circuit, and then a stable voltage is outputted. The clock signal extraction circuit shapes the communication control signal to output a synchronization clock. The low-voltage signal discrimination circuit judges the low-voltage signal to output a low-voltage mark. The energy transition and signal processing circuit of series compensation protection system secondary sampling device has the advantages of high energy conversion efficiency, high reliability, low power consumption and data transmission stability.