The invention discloses a signal processing circuit based on a laser foreign matter sorting system. The signal processing circuit comprises a laser scanning system, photomultipliers, a current-to-voltage conversion circuit, a n-stage series connection voltage amplifier circuit, an integrating circuit, an adder and a buffer circuit, wherein by the aid of the laser scanning system, light is projected into a scanned object, and diffused laser is received by more than three photomultipliers; an input end of the current-to-voltage conversion circuit is connected with the photomultipliers, and an output end is connected in series sequentially with the n-stage series connection voltage amplifier circuit and a integrating circuit; multiple channels of integrating circuit signals are transmitted to the adder, then signals of the adder are transmitted to the buffer circuit, and then the signals are sent out. The signal processing circuit has the advantages of being high in scanning accuracy, broad in band, short in building time, high in conversion speed, low in noise, ultra-low in gain error and the like.