The invention discloses an intermediate-band solar absorption semiconductor and a preparation method thereof. The chemical formula of the semiconductor is MgIn2-xNixS4, wherein x is larger than 0 andis smaller than 2, some In atoms in a MgIn2S4 ternary compound is substituted by Ni atoms to obtain MgIn2-xNixS4, then Mg, In, S and Ni raw materials are weighed according to the stoichiometric ratioof the MgIn2-xNixS4, the materials are sealed in a quartz glass tube in a vacuum mode to be heated to 700 DEG C to 800 DEG C to carry out reaction sintering, the temperature is maintained for 24 to 48hours and then the materials are cooled with a furnace, and then the secondary reaction sintering is carried out under the same condition to obtain the semiconductor. The obtained intermediate-band solar absorption semiconductor has multi-bandgap broad-spectrum solar absorption ability, and the development of intermediate-band semiconductor materials and high-efficiency solar cell technology is hopefully promoted.