The microstructure evolution and properties of medium-carbon cast steel alloyed with different Ni contents after tempering at various temperatures have been investigated. The addition of 0.47–1.59 wt.% Ni content results in the formation of 16%–36% retained austenite (RA). The blocky and irregular-polygonal RA mainly forms along the prior austenite grain boundaries, and the tempering temperature does not affect the RA content. The hardness of medium-carbon cast steel is affected by the precipitation of carbides and the hardness of martensite. Excessive RA content is the main cause of intergranular impact rupture and low impact energy. The long-strip carbides formed after tempering at 320 °C would further reduce the impact energy of medium-carbon cast steel. When tempering at 220 and 380 °C, the increase in impact energy is attributed to the formation of rod-like and spherical carbides and the low-carbon martensite. For the mediumcarbon cast steel with high impact energy, its impact-abrasive wear resistance is more excellent. Micro-cutting and delamination are the primary wear mechanisms.