The ancient trees can easily hurt people and buildings around because of its aging or other biological characteristics and negligence in management. This thesis defined the ancient tree爷s risk based on the definition of ecology risk. By analyzing the relationship between risk assessment and management for ancient trees, we built the risk assessment-management system for ancient trees. This thesis also analyzes the ancient tree's risk reason and the risk suffered by things around from aspects of health and management for ancient trees, which helps ensuring the principle of ancient tree's risk assessment,that is the principle of non-absolute, persistent, dynamic and cycle. By dividing the ancient tree's risk assessment into three steps, i. e. the risk identification-quantitative analysis-matrix discriminance, we finally provide the methods to protect and manage the ancient trees.