Thermal　stress　birefringence　is　a　key　factor　affecting　the　stability　of　optical　voltage　sensors.　The　study　of　thermal　stress　birefringence　is　of　great　significance　for　the　development　of　optical　voltage　sensors.　In　this　regard,　this　article　first　analyzes　the　thermal　stress　birefringence　theory　systematically　based　on　the　theory.　Then,　by　adopting　finite　element　method,　ANSYS　software　is　used　to　establish　a　model　of　the　longitudinal　modulation　optical　voltage　sensor,　and　the　thermal　stress　in　the　BGO　crystal　is　simulated　and　analyzed.　Finally,　the　distribution　and　change　law　of　stress　birefringence　in　crystal　are　obtained　by　combining　theory　and　simulation.　The　results　show　that　the　average　linear　birefringence　on　the　central　clear　path　is　4.8004×10-7,　and　the　resulting　phase　delay　is　0.0476　(2.7273deg).　When　the　clear　path　is　off-center,　the　birefringence　will　increase,　and　increasing　the　spot　size　also　increase　the　birefringence.　©　Published　under　licence　by　IOP　Publishing　Ltd.