The development of predictive theories for spin and valley properties in $\mathrm{W}{\mathrm{S}}_2/{\mathrm{CrBr}}_3$ heterostructures requires fundamental understanding of nonmagnetic vacancy effects. Using density functional theory calculations, we find that nonmagnetic vacancies significantly enhance the spin-orbit splitting at the $K$ and $K$′ valleys in the conduction band minimum of monolayer $\mathrm{W}{\mathrm{S}}_2$ (78.2 meV for W vacancies). However, valley splitting remains prohibited due to preserved time-reversal symmetry. By constructing a van der Waals heterostructure with a monolayer ${\mathrm{CrBr}}_3$ magnetic substrate induces weak exchange interactions, generating a minor valley splitting (−0.8 meV). Remarkably, vacancy engineering amplifies this effect: sulfur vacancies (${\mathrm{V}}_1-{\mathrm{V}}_4$) induce valley splitting ranging from 3.2 to 9.0 meV, while specific tungsten vacancies (${\mathrm{V}}_6$) achieve a maximum valley splitting of 13.2 meV. Our findings reveal that vacancy-induced orbital hybridization and asymmetric potential gradients enhance Rashba spin-orbit coupling. Furthermore, the combining between nonmagnetic vacancy symmetry in $\mathrm{W}{\mathrm{S}}_2$ and weak magnetic exchange from ${\mathrm{CrBr}}_3$ establishes an unconventional symmetry protection mechanism for valley splitting enhancement. This defect engineering strategy provides a pathway for designing tunable valleytronic and spintronic devices based on vertical heterojunctions via precise atomic-scale defect control.

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• Density of states
• First-principles calculations
• Spin-orbit coupling
• Spintronics
• Valley degrees of freedom
• Valleytronics