W-12.8wt%Cu-7.2%Pb powders were milled at room temperature and $-100^{circ}C$ to investigate the mechanical alloying behavior of immiscible W-Cu-Pb system and the effect of milling temperature on the extent of alloying and microstructural refinement. W-Cu-Pb powder reached steady state after further extended milling due to Pb addition, compared to the W-Cu system. The cryomilling at $-100^{circ}C$ caused the more refinement of powder particle size, and enhanced the solubility of Cu or Pb in W, compared with milling at room temperature. In W-12.8wt%Cu-7.2%Pb powder cryomilled at $-100^{circ}C$, the monotectic temperature of Cu-Pb as well as the melting temperature of Cu was decreased by refinement of Cu crystalline size, and the most amorphization was occurred after milling for 150 h.