The invention discloses an energy conversion and signal processing circuit for a series compensation protection system secondary sampling device. The energy conversion and signal processing circuit comprises an electric energy and communication control signal separation circuit, a DC-DC (direct current to direct current) conversion circuit, a clock signal extraction circuit and a low-voltage signal discrimination circuit, a light current energy converter converts laser signals into electric energy outputted to the electric energy and communication control signal separation circuit, the electric energy and communication control signal separation circuit separates three output paths, one path outputs the electric energy to the DC-DC conversion circuit, one path outputs communication control signals to the clock signal extraction circuit, one path outputs low-voltage signals to the low-voltage signal discrimination circuit, the DC-DC conversion circuit adjusts, filters and denoises the electric energy and outputs stable voltage, the clock signal extraction circuit is used for shaping the communication control signals and outputting synchronous clocks, and the low-voltage signal discrimination circuit discriminates the low-voltage signals and outputs low-voltage marks. The energy conversion and signal processing circuit is high in energy conversion efficiency and reliability, low in power consumption and stable in data transmission.