The invention discloses NaLaMgWO6:xSm<3+> red phosphor powder for an LED (Light Emitting Diode), and a preparation method of the NaLaMgWO6:xSm<3+> red phosphor powder, and belongs to the technical field of preparation of luminescent materials. The NaLaMgWO6:xSm<3+> red phosphor powder for the LED is prepared by using NaOH.H2O, WO3, La2O3, MgO and Sm2O3 as raw materials. The method has the advantages that the raw materials are simple and easily obtained, the operation is simple, the preparation period is short, and the method is pollution-free and suitable for large-scale industrial production. The prepared NaLaMgWO6:xSm<3+> red phosphor powder which is tested and analyzed by an XRD, an SEM and a fluorescence spectrophotometer is higher in purity, high in crystallinity, uniform in grain size and high in dispersity, where x is equal to 0.01 to 0.05; the coverage range of an emission wavelength is 550 to 680nm, the color purity of red light exceeds 92 percent, and the correlated color temperature reaches 1392K.