GaAs nanowires have widely applied in infrared devices in the past few years. However, the performance of GaAs nanowire photodetectors is strongly limited by the problem of large surface state density. At the same time, onedimensional GaAs nanowire as photosensors for infrared detection has been seldom studied. In this paper, a single GaAs nanowire infrared photodetector have been successfully fabricated and Ar plasma treatment is performed on the device to improve the performance. The treated GaAs nanowire device exhibits high responsivity of 108 A/W, which is about 6 times larger than the original one (~18 A/W). Besides, the external quantum efficiency up to 25312 % and the detectivity up to 9.21×1011 cmHz0.5W-1. At the same time, the response time τr is significantly reduces from 86.40 ms to 3.36 ms, and the recovery time τf is almost remained as 212.48 ms. The significant enhancement is due to the improvement of nanowires surface quality. These results demonstrate that GaAs nanowire is an outstanding material in infrared field devices and plasma treatment is an effective way to realize high performance nanowire photodetectors.