Abstract: In order to study the effect of Zr on the microstructure and properties of Cu-Cr in situ composites, Cu-15Cr and Cu-15Cr-0.24Zr alloys were prepared by vacuum medium frequency induction melting technique. The effects of Zr on microstructure of Cu-15Cr as-cast alloy and microstructure after annealing at different temperatures was studied by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and transmission electron microscopy (TEM). The tensile deformation test of the two kinds of test alloys was carried out, and the thermal stability of the alloy under the final deformation was studied. The experimental results show that the addition of Zr results in the formation of flaky CuZr intermetallics in the as-cast microstructure of the alloy, which inhibit the formation of eutectic Cr phase and make the eutectic Cr content much lower than that of Cu-15Cr alloy. The size of dendritic Cr is refined as well. The test results also show that the addition of Zr significantly improves the thermal stability of the alloy and increases its tensile strength by 100 MPa after annealed at 550 °C for 1 h. Through the calculation of Gibbs free energy (ΔGmix) in the solidification process of the test alloy, it is proved that the addition of Zr reduces the liquid phase separation temperature and decreases the dynamic nucleation driving force of the Cu-15Cr alloy in the process of solidification, which inhibits the formation of eutectic Cr and is consistent with the experimental results of the as-cast microstructure.