The total noises of focal plane array sensors, readout circuit and their coupling noise were theoretically analyzed. The temperature and integral time dependence of the noise were measured and analyzed for large perimeterarearatio of extended wavelength InGaAs FPA (38×500 μm2). The experimental results show that in certain conditions, FPA noise is not proportional to the square root of integral time. The relationship between FPA noise and dark current at different temperature were studied. Results show that the noises mainly come from 1/f noise and the current noise at the input stage of readout circuit.