The invention discloses a calcium aluminate concrete setting accelerator and a preparation method thereof and belongs to the field of chemical industry. The calcium aluminate concrete setting accelerator comprises the following raw materials in percentage by weight: 20%-22% of calcium aluminate powder, 5%-7% of alum sludge, 5% of sodium nitrite, 5% of sprayed concrete viscosifier and 63% of water.The process comprises: firstly, uniformly mixing a formula amount of calcium aluminate powder, alum sludge, sodium nitrite and sprayed concrete viscosifier, and then, delivering the mixture into a smasher for smashing to form powder; and delivering a formula amount of water into a reaction kettle, adding the smashed mixed powder of the calcium aluminate powder, the alum sludge, sodium nitrite andthe sprayed concrete viscosifier into the reaction kettle while stirring, and carrying out uniform stirring to obtain a finished product. After the calcium aluminate concrete setting accelerator is added into concrete, the concrete can be rapidly set, so that the later strength influences are little; and the calcium aluminate concrete setting accelerator is nontoxic and tasteless.