Daytime radiative cooling devices consisting of various materials are used to transmit and radiate heat energy from a target body outward through the atmosphere and into cold outer space, without using external energy and in the presence of sunlight. In this study, a daytime radiative cooling thin film structure is designed to achieve high emission in the atmospheric transparency window (8–13 µm) and a high reflection of solar radiation. Simple and chemically stable inorganic materials of silicon dioxide, silicon nitride, aluminum oxide, and silver are selected for the initial design of the structure, initially having four layers. The needle optimization technique is used to enhance the initial design to acquire a final structural design of 10 layers of the selected materials. The average emissivity of the cooler in the range of 8–13 µm was numerically found to be 94.5% and the average reflectance for the solar spectrum was determined to be 96.3% according to validated calculations. Lastly, a high net cooling performance of 125 W/m2 is theoretically generated by the structure when it is equal to the ambient temperature and a temperature reduction of 8 °C is achieved from the ambient temperature according to validated calculations.