Abstract: To study the effect of sub-zero temperature on the dynamic fracture characteristics of rocks, the red sandstone was collected to make Notched Semi-Circular Bend (NSCB) specimens, and dynamic three-point bending tests were carried out using a modified Separate Hopkinson Bar (SHPB) experimental system at different temperatures. The test results show that the fracture toughness of the rock has an obvious loading rate effect, and the fracture toughness test value increases exponentially with the increase of the loading rate; when the loading rate is certain, the fracture toughness of the rock increases slowly and then rapidly after entering the cryogenic temperature from room temperature. The fracture toughness of the rock reaches its maximum value at -20 °C, and decreases rapidly with further decrease in temperature. The fracture mode and fracture mechanism of the rock were then analyzed, and it was found that the fracture of red sandstone at sub-zero temperature is mainly intergranular rupture and the tearing of the cement, accompanied by a small amount of transgranular rupture. Finally, the mechanism of temperature influence on rock fracture characteristics is discussed, and this research has some reference significance for the analysis of the low temperature effect on rock fracture properties.