The invention discloses a graphene / silicon dioxide / nano zero-valent iron composite as well as a preparation method and application thereof. The preparation method comprises the following steps: after the graphene oxide is subjected to ultrasonic dispersion, adding tetraethyl orthosilicate, drying after magnetic stirring is carried out completely, introducing nitrogen in a tubular furnace for calcination, adding deionized water into the solids obtained through calcination, after ultrasonic dispersion, introducing nitrogen and adding ferrous sulfate heptahydrate, after uniform stirring, and adding a reducing agent for reducing so as to obtain black flocculent precipitates after complete reaction, washing, carrying out suction filtration, drying, grinding and screening through a sieve so as to obtain the graphene / silicon dioxide / nano zero-valent iron composite. The graphene / silicon dioxide / nano zero-valent iron composite prepared according to the preparation method can be applied to the field of water pollution control as an adsorbent, particularly adsorption removal of arsenic pollutants in waste water, and has the advantages of simple and convenient preparation process, high adsorption speed and the like, and in addition, the required raw materials are wide in source, low in cost and high in practical application value.