The invention discloses an aqueous cutting fluid for hard and brittle material multi-line cutting and a preparation method thereof. The aqueous cutting fluid comprises, by weight, 5-20% of ammonium carboxylate, 5-25% of a water-soluble lubricant, 10-20% of an antirust agent, 0.5-4% of a bactericide, 10-20% of a water-soluble anti-wear reagent at extreme pressure, 10-20% of triethanolamine, 0.1-4% of a settling agent, 0.01-0.1% of benzotriazole, 0.01-0.5% of an antifoaming agent and the balance water. The water-soluble lubricant is a mixture of poly(ether ester), glycerol and sulfurized fatty acid according to a weight ratio of (10-45): (3-18): (2-20). The cutting fluid has good integrated performances such as cooling performances, lubricity, settlement performances, defoaming performances, antirust properties and cleaning effects and satisfies hard and brittle difficult-to-cut material batch processing requirements of a multi-line cutting machine. The preparation method of the aqueous cutting fluid has simple processes, can be operated easily, realizes a low cost and can be finished at the normal temperature.