A photoelectric detection circuit used in fiber Bragg grating (FBG) seismic surveying system is researched and designed. The Bragg signal wave reflected by a fiber grating reflector from a broadband light source is very weak. So the detection of weak signal is very difficult and the detection accuracy of the entire seismic demodulation system is also influenced. Based on the general circuit design idea, a photoelectric conversion circuit detecting weak signals is researched and designed. Experimental results show that the noise in the circuit is only 0.19 mv. So the demodulation accuracy and speed of the system are improved.