This paper demonstrates a simple method of monitoring stand needle biomass and its changes in masson pine forest with Landsat TM data. The forest health situation can be known by comparing monitored satellite data with basic data obtained by forest resources investigation. According to the macroscopically monitored results, an experienced forester can predict the development trend of damage and present corresponding protecting strategy. Thus, the task of macroscopic monitoring and predicting forest damages caused by pests can be realized.