An acquisition system of infrared spectrum signal based on field-programmable gate array(FPGA) is introduced. It is designed to implement data acquisition of 64-channel infrared spectrum signal. Altera’s EP2C35 family chip is used as the control unit to realize the analog multiplexers switching, A/D conversion, data access. For weak DC signal of infrared spectrometer, a signal conditioning circuit is designed to restrain noise. Finally, the data is transmitted to upper computer by serial port. A brief introduction is given about every sub modules. By testing, the system has been validated to be reliability, which can detect minimal 0.23 μV weak DC signal and the actual signal to noise ratio can reach 45 dB.