In order to detect the quality change of Panax quinquefolium in different humidity environments, the spectral imaging technology is applied to detect active constituent of Panax quinquefolium, based on the principle that variation of molecular structure causes variation of fluorescence spectrum. Ultraviolet ray source that with a central wavelength of 254 nm is used to stimulate the Panax quinquefolium sample to emit fluorescence. The continuous fluorescent spectrum image within the range 420～680 nm is got by adjustable liquid crystal light filter based spectrum imaging device. The frame differential method is used to extract the effective area of the spectrum cube and draw the characteristic spectrum image. Three Panax quinquefolius samples that are kept in different humidity conditions are detected, and the normalized characteristic spectrum diagram is drew. The characteristic spectrum shows that the change trend of relative intensity of fluorescence of Panax quinquefolium in different humidity environments are similar. Weighted Euclidean distance between comparison products and samples is utilized to show regularity of the change of Panax quinquefolium. The higher the humidity is, the faster the variation of weighted Euclidean distance is. The result shows that in different humidity environments, the active constituent of Panax quinquefolium will change with time, and this kind of change is irreversible.