Abstract: Poly(methyl methacrylate) (PMMA), a resin material renowned for its excellent light transmittance, is widely used in various optical functional materials. This article systematically reviews recent research progress in the material design, synthesis techniques, and performance optimization of optical-grade PMMA. Starting from the principles of atomic refractivity, molecular structure, and mechanisms of light absorption and scattering, it provides an in-depth analysis of the key factors influencing the optical properties of PMMA. The advantages and disadvantages of various polymerization strategies—including free radical polymerization, anionic polymerization, living radical polymerization, and coordination polymerization—are summarized. Special emphasis is placed on the synergistic effects achieved through copolymerization with fluorine-containing monomers, functional copolymerization, blending modification, and nanofiller compounding in enhancing light transmittance, reducing the refractive index, and improving UV shielding and weather resistance. The study demonstrates that modified optical-grade PMMA can significantly broaden its application prospects in high-end optical devices.