The　preparation　of　nanocrystalline　W-Cu　powders　plays　a　significant　role　in　the　production　of　high　-performance　W-Cu　composites.　The　chemical　reduction　method　is　a　promising　approach　for　industrial　nano-powder　synthesis.　However,　the　influence　of　various　reduction　parameters　on　the　morphology　and　grain　size　of　the　reduced　powders,　as　well　as　their　underlying　mechanisms,　have　remained　unclear.　In　this　study,　we　investigated　the　effects　of　reduction　steps,　temperature,　duration,　hydrogen　inflow　rate,　and　copper　content　on　the　grain　size　of　the　composite　powders　and　disclosed　the　related　mechanisms.　Through　optimization　of　reaction　parameters,　W-Cu　powders　with　grain　sizes　below　50　nm　were　obtained.　Moreover,　the　utilization　of　the　synthesized　nanocrystalline　W-Cu　powders　as　raw　materials　yielded　a　bulk　W-20Cu　composite　with　an　ultrahigh　hardness　of　600　HV30.