The invention relates to a spheroidal graphite ausferrite cast iron grinding ball suitable for being used in a semi-automatic grinding machine and a preparation process. The spheroidal graphite ausferrite cast iron grinding ball is prepared from the following components in percentage by mass: 3.2 to 3.9 percent of carbon, 2.30 to 2.93 percent of silicon, 0.96 to 2.80 percent of manganese, 0.21 to 0.90 percent of chromium, 0.11 to 0.60 percent of copper, 0.10 to 0.80 percent of molybdenum, 0.10 to 0.68 percent of vanadium, 0.10 to 0.78 percent of titanium, 0.01 to 0.09 percent of niobium, greater than or equal to 0 and less than 0.05 percent of phosphorus, greater than or equal to 0 and less than 0.03 percent of sulfur, 0.03 to 0.05 percent of magnesium, 0.02 to 0.03 percent of rare earth elements and the balance of iron. The preparation process comprises the following steps: firstly, performing casting forming to prepare a cast grinding ball; secondly, performing thermal treatment on the cast grinding ball to prepare the spheroidal graphite ausferrite cast iron grinding ball. The hardness of the heart part of the spheroidal graphite ausferrite cast iron grinding ball disclosed by the invention is 54 HRC, and the surface hardness is 58 HRC; the impact toughness is 17 to 20 J / cm2; furthermore, the spheroidal graphite ausferrite cast iron grinding ball is higher in processing hardening capacity; in a wear process, a worn layer is processed to be hardened, so that the hardness can be up to 62 to 64 HRC, and the wear amount is 70 percent of that of a general forged ball.