As　a　potential　and　sustainable　construction　material,　ultra-high　performance　concrete　containing　coarse　aggregate　(UHPC-CA)　finds　promising　applications　in　engineering　constructions,　particularly　in　severe　cold　regions.　This　study　conducts　an　experimental　study　to　investigate　the　influence　of　fiber　content　(ranging　from　0.0　%　to　3.0　%)　on　the　uniaxial　compression　and　splitting-tension　failures　of　UHPC-CA　across　a　temperature　range　of　−90　°C∼20　°C.　Through　microstructure　analysis,　the　underlying　mechanisms　and　quantitative　analysis　behind　the　low-temperature　enhancement　effect　and　fiber　reinforcement　effect　on　the　nominal　strength　and　toughness　of　UHPC-CA　were　elucidated.　The　test　results　show　that　as　the　temperature　drops　from　20　°C　to　−90　°C,　nominal　strengths　of　UHPC-CA　monotonically　increase　(with　a　maximum　increase　88.1　%　for　splitting-tension　strength　while　72.6　%　for　compressive　strength),　but　the　compressive　toughness　reduces　with　a　maximum　decrease　54.6　%.　Additionally,　the　incorporation　of　steel　fibers　can　enhance　the　nominal　strengths　and　compressive　toughness,　exhibiting　the　fiber　reinforcement　and　toughening　effects.　Compared　to　the　UHPC　matrix,　all　the　increases　for　nominal　strengths　and　compressive　toughness　of　UHPC-CA　with　2.0　%　steel　fibers　at　room　temperature　are　higher　than　those　at　low　temperatures,　demonstrating　that　the　decreasing　temperature　can　weaken　the　fiber　reinforcement　and　toughening　effects,　which　may　attribute　to　fact　that　the　formation　of　microcracks　(due　to　the　expansion　of　phase　change　of　pore　ice)　in　the　surface　between　steel　fiber　and　UHPC　matrix　at　low　temperatures,　as　observed　in　the　microscopic　test.　However,　as　the　fiber　content　exceeds　2.0　%,　the　splitting-tension　strength　decreases,　thereby　it　is　recommended　that　the　optimal　steel　fiber　content　is　around　2.0　%　for　UHPC-CA　at　low　temperatures.　Finally,　considering　the　quantitative　effects　of　steel　fiber　characteristics　and　temperature,　the　empirical　prediction　models　for　cryogenic　nominal　strengths　were　proposed　and　verified,　which　can　well　predict　compressive　and　splitting-tension　strengths　of　UHPC-CA　with　various　steel　fiber　contents　at　low　temperatures.　This　study　can　provide　an　experimental　data　reference　for　the　safety　design　of　UHPC　structures　and　contribute　to　promoting　the　application　of　UHPC-CA　in　the　engineering　construction　of　cold　regions.　©　2024　Elsevier　Ltd