The invention provides a measurement method for measuring fluorescent film transmittance or a reflectance spectrum. According to the measurement method, firstly a cut-off filter of appropriate wavelength is selected according to the excitation spectral range and emission spectral range of a fluorescent film; by placement of the cut-off filter of appropriate wavelength in front of a detector, a fluorescent emission section from a light coming out of a sample can be filtered off, so that an accurate fluorescent film transmittance or reflectance curve is obtained; the method is simple to operate,accuracy of measurement is high, the applicable area is broad, the method is applied to not only a down-conversion fluorescent film but also up-conversion fluorescent film, namely, the method is applied to measurement of reflectance of the fluorescent film as well as transmittance of the fluorescent film.