Abstract: As a new type of composite material with good mechanical properties and durability, the flexural toughness of ultra-high toughness cementitious composites (UHTCC) is an important indicator to evaluate its mechanical properties. To explore the bending performance of UHTCC materials under an ultra-low temperature environment, five groups of UHTCC materials with different fiber contents were designed. After cryogenic treatment, four-point bending tests were carried out, and the equivalent strength was analyzed. A toughness evaluation method suitable for ultra-low temperature was proposed, which provided the theoretical basis and technical support for the wide application of UHTCC in the field of ultra-low temperature. The results show that the flexural strength of UHTCC increases significantly after ultra-low temperatures. When the temperature decreases to −160℃, the flexural strength of UHTCC increases by 67.67%, but it shows obvious brittleness. In an ultra-low temperature environment, the strength and toughness of UHTCC with 1.5vol% volume fraction are the best, but the performance of UHTCC is slightly reduced after exceeding the optimal volume fraction.