In order to explore the mechanical characteristics and failure characteristics of water-saturated frozen cement mortar with different transfixion degree joints under impact load, a cyclic freezing impact test was performed on six kinds of water-saturated frozen cement mortar specimens with different transfixion degrees (0%, 20%, 40%, 60%, 80%, 100%) by split Hopkinson pressure bar (SHPB), and the microscopic damage of specimens was tested by an MRI analyzer. The results show that the dynamic compressive strength of the water-saturated frozen cement mortar increases first and then decreases with the increase of the number of cycles, with the increase of joint transfixion degree the peak stress showing a clear linear downward trend. An 80% transfixion degree joint specimen has the weakest ability to carry impact loads, and the 40% transfixion degree joint specimen has the strongest ability to carry impact loads. With the increase of joint transfixion degree, there was a similar trend of first decreasing and then rising in the average change of porosity and the change of energy density per unit time index. The joint transfixion degree controls the crack development trend and the final destruction mode of the specimen. With the increase of joint transfixion degree, the failure sequence gradually evolved from pull-shear composite failure to split-tensioned failure.