InAs/GaSb type-II superlattice materials are the preferred materials for the third-generation infrared focal plane detectors. An InAs/GaSb type-II superlattice long-wavelength infrared focal plane device with array size of 320×256 and pixel pitch of 30 μm is reported. At 77 K, the average peak detectivity of the device is 7.6×10¹⁰ cm·Hz^1/2·W^-1, the blind element rate is 1.46%, the response non-uniformity is 7.55%, and the noise equivalent temperature difference (NETD) is 25.5 mK. The calculation shows that the peak quantum efficiency of this device is 26.2%, and the 50% cut-off wavelength is 9.1 μm. Finally, an imaging demonstration of the device is carried out. The results show that the research has laid the foundation for the subsequent development of related devices.