An analogue-signal acquisition circuit with high Signal-to-Noise Ratio (SNR) is introduced based on a cooled infrared focal-plane detector. The source of the circuit noise is analyzed by using the noise analytical method, and the signal transformation path with low noise is created. Moreover, the indexes of the circuit and imaging components are analyzed by carrying out SNR test together with Noise Equivalent Temperature Difference (NETD) test. The results show that: 1) The component of SNR can reach 76 dB, and NETD can reach 17. 5 mK at environment temperature of 300 K;and 2) Less noise is introduced into the signal acquisition process, and the components can detect dim and small targets at a long distance.