Abstract: W-Cu alloys are widely used in high-power electrical and electronic packaging applications due to their combination of high electrical conductivity and high thermal conductivity. However, traditional W-Cu materials are difficult to form a W/Cu network structure with independent and interconnected phases, and grain coarsening caused by high-temperature sintering limits further improvements in their mechanical and electrical properties. In this study, ultrafine composite powders are prepared using the freeze-drying method, and W-Cu and W-Cu- Y2O3 alloys are fabricated using low-temperature sintering technology to systematically investigate the effects of Y2O3 on microstructure and properties. The results indicate that during both solid-phase and liquid-phase sintering, Y2O3 effectively suppressed W grain growth, increased W-W connectivity, improved the reticular distribution of the Cu phase, and promoted the formation of a W-Cu interconnected reticular structure. Owing to the optimized microstructure, the hardness of the W-Cu-Y2O3 alloy reaches 410 HV0.2, which is approximately 11% higher than that of the W-Cu alloy without Y2O3 addition. Meanwhile, the alloy maintains an electrical conductivity above 42 %IACS, achieving a synergistic improvement in mechanical and electrical properties. This study provides a new strategy for microstructural design of high-strength and high-conductivity W-Cu based composites.