A liquid crystal spectrograph is designed to collect Panax quinguefolium′s spectral image based on liquid crystal tunable filter（LCTF）spectroscope. Panax quinquefolium slice is put under UV light, and its fluorescence image is collecteel by the instrument continuously. Panax quinguefolium′s fluorescence effect is obvious during the detection. Corresponding relations are found between fluorescence intensity and saponins which is panax quinquefolium′s effective active ingredient, when the slice of different grades and standards is detected. So a simple, fast, non-destructive method, which can be applied to assess panax quinquefolium′s quality and ingredient, is established. More over, the slice′s fluorescence curve of spectrum and panax quinquefolium′s saponins 3 dimensional distribution spectrum can be obtained, its saponins′s distribution information can also be obtained.