Very long wave infrared(VLWIR) band widely used in remote atmosphere sounding applications is particularly rich in information about humidity, CO2 levels and provides additional information about cloud structure and the temperature distribution. In order to meet the requirements of VLWIR detectors at present stage, a shared readout integrated circuit with memory-function background suppression was designed for its high injection efficiency, large dynamic range, stable detector bias, long integration time and some other advantages. In this design, the share buffered direct injection(SBDI) input circuit was used to minimize pixel area limitation and to maximize the efficiency of memory-function background suppression by 2×2 four neighboring pixels united. The total integration capacitor could reach up to 8.8 pF that has larger capacity, extended integration time, and increased the signal-to-noise ratio (SNR) of infrared focal plane array(IRFPA). At the same time, better contrast and dynamic range were also achieved. The final chip was fabricated with HHNEC CZ6H 0.35 μm 1P4M process technology. The simulation and test results show that the dynamic range is over 90 dB, the linearity is more than 99.9%, the integration time could be extended to 74 μs when the ROIC operates at the temperature of 50 K.