Two alkali-metal sulfamates nonlinear optical (NLO) crystals, Li(NH₂SO₃) and Na(NH₂SO₃), have been obtained through the facile evaporation method. Li(NH₂SO₃) crystallizes in the polar space group Pca2₁ (No.29). The structure of Li(NH₂SO₃) can be described as a 3D network formed by [LiO₄]^7- polyhedral connecting with NH₂SO₃^- tetrahedra through corner-sharing. Na(NH₂SO₃) crystallizes in the polar space group P2₁2₁2₁ (No.19). The structure of Na(NH₂SO₃) can be described as a 3D network formed by distorted [NaO₆]^11- octahedral connecting with NH₂SO₃^- tetrahedra through corner-sharing. The UV-Vis-near-infrared spectra demonstrate that Li(NH₂SO₃) and Na(NH₂SO₃) possessed large optical band gaps of 5.25 and 4.81 eV, respectively. Powder second-harmonic generation (SHG) measurements demonstrate that the SHG intensity of Li(NH₂SO₃) and Na(NH₂SO₃) were 0.32 times and 0.31 times that of KH₂PO₄, respectively. First-principles calculations confirm the nonlinear optical performance mainly derived from the synergistic effect of amino sulfonate anions and alkali metal oxide anionic polyhedra.