The invention relates to a method for preparing a wide bandgap nanometer cadmium sulfide thin film, which comprises the following steps that: indium tin oxide (ITO) glass using as substrates is placed in a reaction container after organic solvent soaking, ultrasonic cleaning and drying, and oxidbillity additives are added into reaction solution; in the reaction solution preparation stage, cadmiumsalt and the same acid radical ammonium salt are added into the container, de-ionized water is then added, when the temperature is heated to 40 to 70 DEG C, the proper amount of weak base aqueous solution (ammonia solution) is added for producing cadmium complex compounds, and the reaction solution in the first step is formed; and the weak base solution is added, simultaneously, the oxidbillity additives are added, the additives are organic peroxide (ROOH), organic peroxyacetic acid (RCOOOH) and 2 percent to 30 percent of oxyful, and the addition quantity of the oxidbillity additives is 1 percent to 10 percent of the mol number of the cadmium salt. At the time, thiourea is then added, the light transmittance and the energy gap of the wide bandgap nanometer cadmium sulfide thin film are obviously improved, and window materials of copper indium gallium selenium batteries or cadmium telluride batteries can be more favorably manufactured.