The present invention relates to a ferromanganese modified straw active carbon adsorbent for As (III) adsorption, and applications thereof. The technical scheme comprises: preparing straw into straw active carbon, adding to nitric acid, carrying out an acidification treatment to obtain acidified straw active carbon, adding the acidified straw active carbon to a metal iron salt and HCl mixing solution, carrying out a reaction at a room temperature for 22-24 h, heating to a temperature of 95-105 DEG C, carrying out a reaction for 6-7 h to obtain iron modified active carbon, mixing a metal manganese salt and the iron modified active carbon, carrying out a reaction at a temperature of 75-85 DEG C, adding a KMnO4 and KOH mixing aqueous solution, carrying out a reflux reaction at a temperature of 75-85 DEG C, and washing he product so as to obtain the target product. According to the present invention, with the ferromanganese modified straw active carbon adsorbent, the As (III) can be selectively recovered from the solution containing the As (III) ions and the impurity metal ions; and the ferromanganese modified straw active carbon adsorbent has advantages of low cost, high selectivity, high adsorption capacity, and the like.