Based on the modified weather resistance of PVC plastics, a series of La1-xCexAlO3 inorganic pigments were synthesized in this study. A single La1-xCexAlO3 (x varies from 0.00 to 0.20) phase replacement solid solution of rhombohedral crystal structure with the addition of more Ce3+ doping. The sample pigments demonstrated a curved rod to spherical particle morphology change as Ce doping amount increased. The analysis by X-ray photoelectron spectroscopy (XPS) demonstrated that the cerium ion chemical valence states in the synthesized samples were + 3 and + 4. The carrier concentration and electron trap theory can be used to understand the variation in near-infrared reflectance of La1-xCexAlO3 pigment powder from 72.55% to 83.35%. Electric charge transfer (La 3d ↔ Ce 3d) can be used to describe how the La1-xCexAlO3 pigment shifts from white to orange to yellow. When PVC plastic is modified with pigment, the near-infrared reflectance varies from 52.87% to 61.63%. Inner surface temperature of La1-xCexAlO3/PVC composite plastics can be lowered by 8.5–13.7 °C, and the weather resistance of the modified PVC plastic is greatly increased. In conclusion, the modification of PVC plastics with La1-xCexAlO3 inorganic pigments can significantly reduce the surface temperature of plastics and prolong their service life.