The invention discloses a large-size high-infrared transmittance CdS single crystal growth method. The method comprises the following steps: purifying CdS raw materials: putting weighed raw materials into an ampoule bottle, mounting a sapphire growth substrate and a heat-conducting stick at the opening of the ampoule bottle, arranging a growth zone on a quartz support tube, putting into a quartz heat-preserving outer tube altogether, and then integrally putting into a purification furnace for purification; growing CdS single crystals: putting weighed polycrystal materials into the ampoule bottle, and adding weighed Cd granules into the polycrystal materials; and after putting CdS seed crystals at the opening of the ampoule bottle, evacuating the heat-conducting stick covered with the sapphire, and putting into a single crystal growth furnace for single crystal growth. The process is simple, short in growth cycle and low in cost. The CdS single crystal grown by the method has a large size, and the diameter can be up to 53mm; the single crystal has high transparency and favorable infrared transmittance, is less prone to cracking, and can be preserved for long time at room temperature and normal pressure, and the infrared transmittance at the 2.5-5mu m part can be up to 71.5%.