In　this　work,　cation　vacancies　induced　the　tetrahedral　distortion,　enhancing　the　second　harmonic　generation　(SHG)　response　in　the　diamond-like　(DL)　structure　compounds.　Concretely,　the　high　valence　and　electronegativity　of　P5+　were　introduced　to　substitute　the　Ge4+　in　Cd4GeS6,　which　shows　a　general　SHG　response　of　1.1　x　AgGaS2　(AGS)　at　2050　nm.　Thus,　the　isomorphic　defective　DL　Cd3.5PS6　was　obtained　with　inherent　Cd2+　vacancies,　leading　to　an　8.5-fold　increase　in　[CdS4]　tetrahedral　distortion　degree　than　Cd4GeS6.　As　a　result,　Cd3.5PS6　has　a　high　SHG　response　of　2　x　AGS　at　2050　nm　and　a　laser-induced　damage　threshold　(LIDT)　of　9.4　x　AGS.　Furthermore,　equivalent　Hg2+　substitution　concentrates　Cd2+　vacancies　at　the　Cd(2)　site,　leading　to　a　2.66-fold　[CdS4]　tetrahedral　distortion　degree　than　Cd3.5PS6.　Consequently,　Hg0.5Cd3PS6　possesses　a　high　SHG　response　of　2.73　x　AGS　at　2050　nm　and　LIDT　of　5　x　AGS　with　a　birefringence　of　0.076@2050　nm.　The　results　indicate　that　the　cation　vacancies　and　radius　scale　of　mixed　atoms　provide　effective　ways　to　design　high-performance　nonlinear　optical　crystals.