In　high-temperature　rock　engineering　projects,　rocks　are　subjected　to　external　loads.　Studying　the　cracking　behavior　of　thermally　damaged　rock　under　uniaxial　loading　is　of　great　significance　to　engineering.　In　the　present　study,　real-time　computed　tomography　(CT)　scanning　was　performed　on　thermally　damaged　granite　subjected　to　compression　loading　to　observe　the　evolution　of　spatial　three-dimensional　(3D)　microcracks　and　planar　two-dimensional　(2D)　microcracks.　The　porosity　and　crack　length　were　further　introduced　to　quantify　microcracking　behavior.　The　effects　of　the　load　on　the　3D　microcrack　volume　distribution　and　the　length　of　2D　microcracks　with　different　orientations　were　discussed.　The　results　show　that　real-time　CT　imaging　intuitively　presents　the　evolutionary　process　of　realistic　microcrack　morphology　during　loading.　As　the　load　level　increases,　the　porosity　of　the　specimen　and　the　total　length　of　2D　microcracks　experience　stages　of　slow　decrease,　slow　increase,　and　rapid　increase.　The　proportion　of　microcracks　with　larger　volumes　decreases　and　then　increases　as　the　load　level　increases.　In　the　slice　parallel　to　the　loading　direction,　the　length　of　microcracks　within　an　angle　range　of　30　degrees-90　degrees　to　the　loading　direction　decreases　as　the　load　level　increases.　In　the　slice　perpendicular　to　the　loading　direction,　the　microcrack　length　distribution　exhibits　obvious　anisotropy　as　the　load　level　increases.