The invention relates to a nickel slag grinding system which is characterized by mainly comprising a feeding bin, a quantitative feeding machine, a column mill vibrating screen, a belt conveyor, a strong magnetic separator, a nickel slag vertical mill, a dry magnetic separator, a bag type dust collector, a main exhaust blower and a hot blast heater system. Nickel slag with the water content being not more than 5 percent and the granularity being less than 60mm is sent to the column mill to be ground by using the nickel slag grinding system, so that fine powder with the water content being above 90 percent and the granularity being below 5mm is obtained, the fine powder is subjected to iron separation through the strong magnetic separator after being screened, and is dried and ground in the nickel slag vertical mill after being subjected to iron removal. Meanwhile, after large particles containing iron are thrown out by a millstone, and are fed into the mill again after being subjected to iron removal through the dry magnetic separator. Finally, after multiple times of circulating grinding, a finished nickel slag micropowder product with a specific surface area of 4200-4500 cm<2>/g is obtained, and the finished product passing through the bag type dust collector is sent to a finished product library through an air conveying chute, and waste gas is discharged into atmosphere through a chimney. The nickel slag grinding system has the advantages of large yield, high grinding efficiency, low use cost and operation cost, remarkable electricity saving effect, and increasing of economic benefits.