As　the　research　on　air　temperature　field　in　large　space　structure　is　relatively　scarce,　computer　simulation　was　performed　by　FDS　program　for　fire　cases　to　study　the　air　heating-up　process　for　large-space　structure　under　fire.　The　effect　of　smoke　emission　on　fire　temperature　field　is　considered.　Mathematical　model　of　temperature　field　related　to　time　has　been　established.　The　related　parameters　and　the　evaluation　function　of　the　fitting　results　(the　square　of　related　coefficient　R2)　are　obtained　by　a　nonlinear　curve-fitting　method　with　MATLAB　program.　The　coefficient　of　temperature　rise　velocity　r　and　the　equilibrium　temperature　θm　are　the　main　parameters　related　to　the　characteristics　of　space　temperature　field.　As　the　value　of　R2　for　the　heating-up　curve　calculated　by　numerical　simulation　and　the　mathematical　model　is　more　than　0.95,　the　mathematical　model　is　simple,　practical　and　credible.