Underground　thermal　engineering　such　as　geothermal　exploitation　usually　involves　the　response　of　impact　loads　due　to　the　drilling　operation　and　blasting　load.　This　study　investigated　the　dynamic　mechanical　properties　and　fragmentation　characteristics　of　granite　sub-jected　to　thermal　cycling　under　natural　cooling,　water　cooling,　and　liquid　nitrogen　cooling.　Firstly,　split　Hopkinson　pressure　bar　tests　were　performed　on　granite　under　three　different　cooling　methods　to　study　the　dynamic　mechanical　parameters　with　thermal　cycles.　Sub-sequently,　the　damage　factors　were　calculated　to　evaluate　the　damage　on　granite　and　the　relationship　between　damage　and　stress.　Finally,　the　granite　fragments　after　impact　were　sieved,　and　the　fractal　dimension　and　average　fragment　size　were　introduced　to　analyze　the　frag-mentation　characteristics.　The　results　demonstrate　that　the　degradation　of　dynamic　mechanical　properties　mainly　occurs　in　the　first　four　thermal　cycles;　with　the　increase　of　damage　factor,　the　stress　decreases　linearly　under　the　three　cooling　methods,　and　the　damage　caused　by　liquid　nitrogen　cooling　to　granite　is　the　most　significant,　followed　by　water　cooling.　Fragments　of　granite　change　from　axial　splitting　failure　to　a　more　complex　composite　failure　mode.　In　addition,　with　the　decrease　of　the　average　fragment　size,　the　fractal　dimension　of　the　granite　gradually　increases,　resulting　in　the　higher　fragmentation　degree　and　the　better　uniformity　of　fragmentation.