Abstract: With 12 American LANDSAT TM images taken in Guangdong Province in late 1997 and early 1998 as information source and based on GIS, the present paper studied how well the TM spectrum values and their ratios could indicate the real conditions of the stands with the method of principal component analysis. Eight types of stands were analyzed, including mason pine, Chinese fir, eucalyptus, soft bark, sclerophyllous and other broadleaved stands, mixed coniferous stand and mixed coniferous-broadleaved stand. Results showed that the 4th principal component indicated the messages about mean tree height, mean diameter at breast height, age class and canopy closure, the first three principal components of most stands revealed spectrum values and their ratios, while the other principal components had different indications among the stands studied.