Spinodal phase separation in SMART materials based on binary W-Cr with alloying 1 elements Y and Zr is systematically investigated by a combination of Density Functional Theory with Cluster Expansion Hamiltonian and large-scale Monte Carlo simulations with thermodynamic integration. Comparing alloying of Zr with those from Y, it is shown that there is a significant difference in the average short-range order between W and Zr which changes from positive to negative from 500 K to high temperature in W70Cr29Zr1 alloys comparing with the positive SRO between W and Y in W70Cr29Y1 ones. The change, however, didn’t affect the segregation behaviour between W and Cr in whole range of temperature between these alloys. Importantly, it is found that co-segregation of both Y and Zr due to the negative SRO between them in W70Cr29Y0.5Zr0.5 increases the W-Cr positive SRO closer to the binary W70Cr30 within all considered systems. Our modelling results reveal a significant impact on spinnodal phase segregation of W and Cr in designing SMART materials for DEMO device of future fusion power plants. It also provides a fundamental understanding of radiation resistance phenomena in neutron irradiated in self-passivating alloys from the recent experimental observation.