The Cu-10Cr-0.4Zr in situ composite microwires were prepared by cast and cold drawing procedure. Deformation processing and mechanical properties of Cu-10Cr-0.4Zr composites were investigated. The results showed that the additional 0.4wt. %Zr in the Cu-10Cr in situ composite microwires gave birth to smaller as-cast Cr phases, which led to refined filaments in the matrix at higher drawing strains. As the drawing strains increased, the Cr filaments were constrained to fold or twist (even overlapped together) on longitudinal sections, and the Cr filaments become homogeneity and refinement at the longitudinal sections at the same time. At η=6.2, the thickness of Cr filaments reached 250-300nm, and the ultimate strength of Cu-10Cr-0.4Zr composites reached 1089 MPa. And the predicted strength using Hall-Petch equation was 1037 MPa, which was in reasonably good agreement with the observed strength (1089 MPa).