A　new　compound　with　mixed　valence　of　tellurium,　namely,　NaYTe2O7　has　been　successfully　synthesized　by　the　high−temperature　solid　state　reaction　through　adopting　substitution　strategy.　This　compound　crystallizes　in　the　monoclinic　space　group　of　P21/n,　and　features　two−dimensional　[Te2O7]4−　layer　which　is　composed　of　TeVIO6　octahedra　and　TeIVO4　dispheniods.　The　anionic　layers　stack　along　[101]　direction　and　interlinked　by　Y3+　and　Na+　cations.　The　opposite　arranged　active　lone　pairs　of　TeIV　and　the　layered　anionic　structure　together　induce　the　large　birefringence　which　is　estimated　to　be　0.18　at　1000　nm　by　first−principle　calculation.　This　result　indicates　that　the　proper　arrangement　of　lone　pairs　and　directional　covalent　structure　favor　the　increase　of　crystal＇s　birefringence.　Furthermore,　optical　diffuse　reflectance　spectrum,　infrared　spectrum,　thermal　analysis　and　DFT　calculations　were　also　accomplished.　©　2019　Elsevier　B.V.