The　investigations　on　the　influence　of　geometric　dimension　on　concrete　failure　at　normal　temperature　have　made　a　fruitful　progress,　while　the　investigations　on　the　size　effect　of　concrete　at　elevated　temperature　approach　blank.　For　investigating　the　influence　of　elevated　temperature　and　dimension　on　static　and　dynamic　failures　of　concrete,　a　3D　thermo-mechanical　coupling　method　considering　the　meso-structural　characteristics　of　concrete　and　the　strain　rate　effect　of　material　was　established.　Flexural-tensile　failure　analyses　of　concrete　beams　with　different　geometric　dimensions　were　conducted　after　heat　conduction　analysis.　The　results　reveal　that　the　speed　of　the　heat　transfer　is　relatively　fast　in　small-sized　concrete　and　the　heat　conduction　behavior　quickly　approaches　an　equilibrium　state.　There　is　a　significant　degradation　behavior　on　dynamic　flexural-tensile　strength　for　concrete　exposed　to　fire.　The　elevated　temperature　can　weaken　the　strain　rate　hardening-effect　of　concrete.　At　normal　temperature,　the　influence　of　geometric　dimension　on　dynamic　flexural-tensile　strength　can　be　weakened　at　low　strain　rates　while　there　is　a　reverse　size　effect　at　high　strain　rates.　At　elevated　temperature,　with　the　increasing　geometric　dimension,　the　flexural-tensile　strength　first　decreases　and　then　increases　at　low　strain　rates　while　the　strength　increases　steadily　as　subjected　to　high　strain　rates.