Studying　crystal　anisotropy　is　of　great　importance　for　understanding　the　thermal-mechanical　coupling　behavior　of　crystalline　rocks　in　deep　underground　engineering.　In　this　study,　a　microscopic　parameter　calibration　method　incorporating　the　size　effect　is　proposed.　Subsequently,　a　thermal-mechanical　coupling　model　accounting　for　the　quartz　crystal　anisotropy　is　established　to　investigate　the　thermal-mechanical　coupling　behavior　of　monomineral　quartzite.　The　results　show　that　thermal-induced　microcracks　are　exclusively　distributed　along　crystal　boundaries,　and　initiate　preferentially　from　crystal　boundaries　with　a　larger　average　linear　thermal　expansion　coefficient,　eventually　leading　to　the　formation　of　a　crack　network.　With　the　increase　in　temperature,　the　peak　strength　of　monomineral　quartzite　increases　slightly　at　first　and　then　decreases　rapidly,　and　the　transition　threshold　temperature　is　200　degrees　C.　Both　elastic　modulus　and　Poisson＇s　ratio　show　a　monotonic　pattern,　with　abrupt　changes　occurring　at　200　and　300　degrees　C,　respectively.　The　monomineral　quartzite　exhibits　a　significant　compaction　stage　under　uniaxial　compression,　and　the　ductile　strengthening　critical　temperature　for　monomineral　quartzite　are　between　400　and　500　degrees　C.　The　quartz　crystal　anisotropy　leads　to　an　anisotropic　distribution　of　inclination　angles　for　tensile　microcracks　under　high　temperatures　while　having　no　obvious　effect　on　the　shear　microcracks.　In　addition,　the　average　size　of　fragments　generated　under　uniaxial　compression　is　influenced　by　thermal　cracking,　demonstrating　an　initial　decrease　followed　by　an　increase,　and　the　distribution　of　fragment　sizes　is　solely　correlated　with　the　temperature,　which　is　more　concentrated　with　the　increase　in　temperature.