Water and energy metabolism of plants is very important actions in their lives. Although the studies about these actions by using thermography were often reported, seldom were found in detecting the health status of forest trees. In this study, we increase the measurement accuracy and comparability of thermo-images by creating the difference indices. Based on it, we exam the water and energy status in stem of Chinese arborvitae (Platycladus orientalis (L.) Franco) by detecting the variance of far infrared spectrum between sap-wood and heart-wood of the cross-section of felling trees and the cores from an increment borer using thermography. The results indicate that the sap rate between sapwood and heartwood is different as the variance of the vigor of forest trees. Meanwhile, the image temperature of scale leaves from Chinese arborvitae trees with different vigor is also dissimilar. The far infrared spectrum more responds the sap status not the wood percentage in comparing to the area rate between sapwood and heartwood. The image temperature rate can be used in early determining the health status of Chinese arborvitae trees. The wood borers such as Phloeosinus aubei Perris and Semanotus bifasciatus Motschulsky are the pests which usually attack the low health trees, dying trees, wilted trees, felled trees and new cultivated trees. This measuring technique may be an important index to diagnose the health and vigor status after a large number of measurements for Chinese arborvitae trees. Therefore, there is potential to be an important index to check the tree vigor and pest damage status by using this technique. It will be a key in the tending and management of ecological and public Chinese arborvitae forest.