The invention discloses a lumefantrine isomer and a preparation method thereof, specifically a preparation method and uses of (RS,Z)-2-dibutylamino-2-[2,7-dichloro-9-(4-chlorobenzylidene)-9H-fluorene-4-yl]ethanol, wherein 2,7-dichlorofluorene-4-oxirane is used as a starting raw material and a selective ring-opening reaction, a substitution reaction, a deprotection reaction and a condensation reaction are performed to prepare the high-purity lumefantrine isomer. According to the present invention, the reaction conditions of the method are mild and simple, and the obtained lumefantrine isomer is the important impurity of the lumefantrine bulk drug, and is the impurity reference substance of the quality control.