The invention discloses a method for enhancing optical absorption of CdIn<2>S<4>. Specifically, a non-transition metal atom Sn is doped into CdIn<2>S<4> of a semiconductor, and a bandgap of the CdIn<2>S<4> is induced to generate an intermediate impurity band to generate a new optical absorption pathway, thereby achieving the target of enhancing optical absorption of the CdIn<2>S<4>. The method specifically comprises the steps of weighing raw materials of Cd, In, S and Sn according to a stoichiometric ratio of CdIn<2-x>SnS<4>; packaging the raw materials into a quartz glass tube in vacuum, heating the raw materials to 700-800 DEG C for reaction sintering; carrying out heat preservation for 24-48h and then carrying out furnace cooling; and carrying out secondary reaction sintering. According to the method, the optical absorption capability of the CdIn<2>S<4> is enhanced; and the method has a broad application prospect in the fields of photocatalysis and a photovoltaic cell.