Abstract: Through the dynamic impact test of pressure bar (SHPB), the dynamic mechanical properties of red sandstone under negative temperature were studied, and the influences of different negative temperature on rock strength properties, fractal dimension and dissipated energy were analyzed, and the reasons for the deterioration of rock dynamic mechanical properties under low negative temperature were analyzed in combination with micro-fracture morphology.The research shows that low negative temperature will cause "frostbite" of red sandstone. Under high strain rate loading, the rock will quickly lose its bearing capacity and its dynamic mechanical strength will drop sharply.The dissipated energy W_L of frozen rock specimen is positively correlated with the fractal dimension D, and closely related to the macroscopic failure characteristics. In other words, the greater the dissipated energy is, the more seriously the rock is broken, and the greater the corresponding fractal dimension is.Fracture morphology analysis shows that the lower negative temperature can make the red sandstone interface between internal material generate a large number of cracks, the crack tip poor, to instability under high strain rate loading low stress brittle fracture the composition of cement more susceptible to negative temperature effect, so the dynamic load and negative temperature cement, cause the collapse of the red sandstone as a whole.