The present invention discloses a method for preparing sucralose-6-acetate in a biphasic liquid-liquid system. The method comprises slowly dropwise adding an inert non-polar solvent containing a chlorinating agent to an N,N-dimethyl formamide (DMF) solution of sucrose-6-acetate; then reacting the biphasic liquid-liquid mixture at a certain temperature for 9-20 hours; cooling the system to room temperature after stopping heating, and settling the solution to form layers, an upper layer being an inert non-polar solvent layer, and a lower layer being a DMF solution layer containing the product; hydrolyzing, neutralizing, and filtering the lower layer to obtain a filtrate, and then concentrating the filtrate to obtain a concentrate; dissolving the concentrate in water, and obtaining the product by extraction using ethyl acetate and crystallization, the inert non-polar solvent being an alkane solvent containing 8-18 carbon atoms that is not mutually soluble with DMF. The method has a high product yield, and can significantly reduce the decomposition of DMF, thereby reducing costs.