Abstract: Classification of decision tree is an important method in data mining. The basic ideas and common algorithms of decision tree algorithm are discussed， the decision tree mining is applied to students′ mental health data analysis， and to analyse the impacting factors on students′ mental health.With the C5.0 algorithm， performed by Clementine 12.0， the decision tree mining model was constructed， the data flow was also set， with continuous test and analysis， discovered that compulsion was the main symptom which impacted the mental health of students. To view the model with compulsion as the classification object， it can be find out that anxiety and social relationship also have big influences. The target attribute were set as anxiety_degree and social relationship_degree， output variables were set as the left nine factors， dug out the main factors which cause the compulsion， to provide the reference to the mental health domain.

Key words: data mining, decision tree, mental health, student