Abstract: This study investigated the effects of rare earth Y addition on the carbide morphology, distribution, and mechanical properties of Cr12MoV cold work die steel using optical microscopy (OM), scanning electron microscopy (SEM), electron probe microanalysis (EPMA), and transmission electron microscopy (TEM). The results showed that the addition of rare earth Y significantly refined the network structure of as-cast eutectic carbides (M₇C₃) and inhibited secondary dendrite growth. After forging, the carbide distribution became more uniform. Following spheroidizing annealing, Y promoted the spheroidization of M₇C₃ carbides and increased the quantity of M₂₃C₆ carbides by 34%. Mechanical property tests indicated that after Y modification, the annealed hardness of the Cr12MoV steel increased by 1.5 HRC, while tensile strength, yield strength, and elongation were improved by 43.2 MPa, 80.2 MPa, and 1.7%, respectively, demonstrating enhanced strength without sacrificing toughness. Fracture analysis revealed a significant increase in the number of dimples, further confirming that rare earth Y effectively improved the material’s strength and toughness.