A functionalized polyacrylonitrile fiber PANODF modified by ethanolamine and dithizone is successfully prepared to selectively identify Ag+ by colorimetric method and then reduce various dyes in situ cooperating with NaBH4. The color of functionalized fiber changes from orange to bright red when it is soaked in solution with Ag+ ions. It's even more satisfying that no relevant color change of the fiber has been observed in the solution of other 12 kinds of metal ions. Obvious color change can occur within 3 min and the detection limit can reach 1 ppm for Ag+. In addition, the process of recognizing Ag+ will not be interfered by other ions in the real water sample. Moreover, the functionalized fiber can be reused up to 10 times for Ag+ recognition. Additionally, the Ag+ ions absorbed on the fiber can be reduced to Ag0, creating a new fiber (PANOD-Ag0F) that can be used as a catalyst to reduce various dyes in situ with NaBH4. The experimental results show that the six kinds of dyes can be quickly reduced to the colorless and less-toxic substance under the condition of NaBH4 as the reducing agent and PANOD-Ag0F as the catalyst. The catalytic reduction capacity of PANOD-Ag0F can still reach more than 99 % when it is recycled for 10 times, which proves the practical application potential of the functionalized fiber.