In order to improve the detection sensitivity of the laser seeker, the relationship between the bandwidth of the quadrant detector amplification module and the detection sensitivity of the laser seeker was fitted by numerical simulation. The influence of the pulse width of the guided laser irradiation on the bandwidth design of the quadrant detector amplification module was quantitatively analyzed. The bandwidth design method of quadrant detector amplifier was proposed, and the effectiveness of the method was verified by the exam with a laser seeker. The results show that the bandwidth design method of quadrant detector amplifier can effectively reduce the minimum detectable power of laser seeker. After the optimization design of the laser seeker quadrant detector amplifier, the minimum detectable power of the laser seeker can be reduced by about 60% compared with the original design, and the detection sensitivity of the laser seeker can be effectively improved. This study provides a reference for the design of photoelectric detection system of laser seeker.