The invention relates to the technical field of mineral grinding, in particular to a slag grinding aid. The slag grinding aid is prepared from, by weight, 25-40 parts of isopropanolamine, 10-20 parts of butyl acetate, 8-18 parts of ethylene glycol monobutyl ether, 8-15 parts of bamboo vinegar, 2-7 parts of cellulose ether, 1-5 parts of carrageenan and 33-43 parts of deionized water. According to the slag grinding aid, the grindability of mineral powder and the activity index of superfine slag powder can be improved, the yield of a grinding machine can be increased, the power consumption per unit time is reduced, and the storage period can be also prolonged.