In order to realize large scale, high spatial resolution and high spectral resolution, mechanical assembly technology was usually adopted to realize Long Linear assembly. The large cold plate of 120 mm was achieved through the mechanical assembly technology of two thermoelectric coolings. Packaging of Long Linear InGaAs focal plane array assembly with 4 000 pixels was adoped through the mechanical assembly technology. Temperature uniformity distribution of the Long Linear, the coplanar error of FPAs, and the engineering reliability of the assembly were studied. The temperature uniformity was controlled at ±0.4℃, the focal plane array coplanar error was controlled inside ±0.020 mm by mechanical assembly of thermoelectronic coolings, thermal analysis, selection of coolings material, tolerance control of component and micro regulation etc. The Long Linear InGaAs focal plane array shortwave infrared assembly had passed the impact and random vibration test, the focal plane array coplanar error was nearly unchanged. At last, a clear ground-imaging in the camera was abtained.