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It is urgent to develop new copper alloys for future fusion reactors (e.g. DEMO and CFETR). This work involved the design and fabrication of an alloy, Cu-0.8Cr-0.12Zr-(0.05Si), with increasing high-temperature softening resistance by thermo-mechanical treatment. The influence mechanism of Si on its mechanical properties and softening resistance at high temperature was investigated. The peak-aged Cu–Cr–Zr alloy containing Si exhibits higher ultimate tensile strength of 622 MPa, yield strength of 588 MPa with a considerable elongation of 17% and electrical conductivity of 76% IACS. The dislocation and Orowan strengthening trigged for finer Cr precipitates are proven to be the main reasons for the improvement in strength. Moreover, the increase in elongation originates from the deformation twins due to the lower stacking fault energy, as confirmed by the first principles. Meanwhile, the addition of Si can significantly improve the high-temperature softening resistance of the alloy. The main reason is that the growth of Cr precipitates is suppressed by adding Si, and its pinning effect on the boundary is better, thereby inhibiting the occurrence of recrystallization. [ABSTRACT FROM AUTHOR]