The invention discloses a visible-light-driven photocatalyst and a preparation method and an application thereof. The preparation method mainly comprises the following steps of: weighing AgNO3 and Na2HAsO4 respectively, putting into different beakers, dissolving with deionized water, and charging into two separating funnels respectively; preparing ammonia water of a certain concentration by using stronger ammonia water; reacting an AgNO3 solution with an Na2HAsO4 solution under a room-temperature magnetic stirring condition by adopting a parallel flow precipitation method; dripping at a speed of 2-3 drips per second while controlling the pH of a mixture at 5-8 by using ammonia water, and continually stirring magnetically at the room temperature for two hours after dripping; and repeatedly washing the prepared orange-yellow precipitate, and drying at the temperature of 60 DEG C to obtain a reddish-brown powdery product, i.e., the Ag3AsO4 photocatalyst. The preparation method disclosed by the invention is simple, and contributes to large-scale popularization and application; conditions in the method are mild, and are easy to control; and the prepared Ag3AsO4 photocatalyst has high activity, and is suitable for degrading organic pollutants under visible light.