In summary, based on FHSP-NLO calculations of tin-containing sulfides compounds identified Y₃CuSnS₇ as a promising NLO material. Through substituting Y with rare-earth elements, the research was extended to its isomorphs Sm₃CuSnS₇ and La₃CuSnS₇. Among them, La₃CuSnS₇ demonstrates superior comprehensive performance compared to AGS, featuring an experimental bandgap of 2.72 eV, a LIDT of 1.7 times that of AGS, a birefringence of 0.034 at 546 nm, and a SHG intensity approximately 2.5 times that of AGS. It also exhibits the strongest SHG response within the reported Re₃M^ⅠM^ⅣS₇ family. The theoretical calculations reveal that SHG primarily originated from [LaS₆] and [CuS₃] units. The reports on these three compounds will offer further insights into exploring IR-NLO crystals of tin-containing sulfides and provide guidance for obtaining excellent candidate materials in future development.