as one of the most common species on Earth, tree plays an essential role in protecting ecological environment. Without trees large loss will occur in all aspects, such as soil erosion and climate warming, which will also harm human activities. In this case, it is vital to keep tree healthy growth to prevent the potential hazard to human. A Narrow Band-Internet of Things (NB-IoT) based tree health monitoring system is proposed in this study. It could provide effective guidance and monitoring for arborists to keep trees healthy. In this system, data collection of four various environmental features, which are thought as crucial factors in tree health, is achieved by relative sensors. Since NB-IoT has the advantages of low-power consummation and large coverage area, it is adopted to provide the transmission means for collected data and forward them to the sever for further analysis in this study. As an efficient method solving classification problems with small amount of data, K-nearest neighbors (KNN) suits this study well and is adopted. A tree health monitoring system is established finally, in which the data of environmental features are used as input to gain the health state of trees as output and the accuracy of this system could achieve 87.3%.