A novel selective multilayered periodic grating radiator (MPGR) was proposed in the paper, which is composed of Al2O3, SiO and SiO2 on an Al substrate. The influence factors on the radiative cooling power of the selective structure were studied by orthogonal test method, including the grating period, duty cycle and grating height. The spectral absorptivity and electromagnetic field of the MPGR were analyzed by using the rigorous coupled wave analysis (RCWA). Moreover, the MPGR was optimized by using the particle swarm optimization (PSO) algorithm. The results shown that the grating height has the greatest impact on the periodic grating structure. The optimized MPGR obtained a wide and high absorption peak in the atmospheric transparency window, which due to the coupling between SPPs and MPs of different modes. The emissivity of the designed grating presents a weak dependence on the incident angle. The optimized selective MPGR achieves a net cooling power of 118.17 W/m2 at nighttime ambient temperature of 300 K.