The invention discloses a preparation method of a copper-indium-gallium-selenium alloy. The preparation method comprises the following steps of: a, mixing: uniformly mixing four raw materials including copper, indium, gallium and selenium according to a molar ratio of 1:(0.6-0.9):(0.3-0.6):(1.9-2.2); b, sealing: filling the mixed material of the copper, indium, gallium and selenium into a reaction kettle, vacuumizing, introducing argon into the reaction kettle, and sealing the reaction kettle; c, heating: putting the reaction kettle into a heating furnace, wherein when the temperature of the reaction kettle reaches 300 DEG C by heating, the reaction kettle starts to perform rocking motion along with the heating furnace, and when the temperature of the reaction kettle is raised to 1250 DEG C, the temperature is kept constant for 2-6 hours; d, cooling: stopping the movement of the heating furnace when the temperature of the reaction kettle is lowered to the room temperature, opening the reaction kettle to release the argon, and taking the alloy out of the reaction kettle to obtain the copper-indium-gallium-selenium alloy. According to the preparation method of the copper-indium-gallium-selenium alloy, pollutions caused by leakage to equipment and the environment are avoided, the copper, indium, gallium and selenium can react fully, and the probability of explosion and strength of explosion are reduced.