The invention discloses a quenching treatment process of a medium chromium cast ball and the process comprises the following steps: the medium chromium cast ball discharged from a furnace is directly filled in a charging basket to be hung to a trolley stove and tempered, the tempering temperature is 700-720 DEG C and the tempering time is 10-10.5h; and after tempering, the furnace door is opened for natural cooling. The ratio of components in the medium chromium cast ball is 1.9-2.2 percent of carbon, and the diameter of the medium chromium cast ball is over 100mm. By regulating the chemical constituents of the medium chromium cast ball and improving the technology, the process improves the toughness of products, brings down the percentage of damage of medium chromium cast balls with the diameter over 100, boosts the grinding quality of ferrous powder, reduces production cost and creates economic benefits for enterprises.