In order to test the distribution of active constituent of traditional Chinese medicine and to evaluate the quality of medicinal part effectively, spectral imaging analysis technology was used, and rhizoma coptidis pieces were tested as an example. First, the fluorescence spectral cube was taken, and the spectral curve of 3 different medicinal parts of the piece was obtained; second, spectral images were reconstructed by principal components analysis method, and the differences of 3 medicinal parts on the first few principal components were focused; third, the first component image was divided by the threshold method, then the distribution and relative content of 3 medicinal parts were obtained. The results show that spectral imaging analysis technology can provide the distribution of the active constituent, which can be used as the criterion of selecting medicinal parts. The testing course is nondestructive and rapid.