The read of various contents of case files suffers from information overload and knowledge disorientation. To solve this problem， an automatic construction method of knowledge forest for electronic case files was proposed with the topic facet trees and the cognitive relationships between topics as the intellectualized representation of the case files. Firstly， different types of files were classified and divided into multiple fragments of single topic by the fragmentation preprocessing of the case files. Then， different information extraction methods were adopted for different fragments， and knowledge fusion was used to merge the synonymous information. After that， the topic faceted trees were constructed by combining the ontology structures and rules and the topic relationships were extracted. Finally， the topic faceted trees and the topic relationships constructed by the knowledge forest were stored in the database to realize the visualization of the knowledge forest. Experimental results show that the proposed method can display the case file information completely and accurately， organize scattered knowledge fragments together with complex case file topics， making it possible to achieve the reading file goal by selecting some case file topics and a small number of case file fragments， and alleviate the burden of complete browsing case file contents to realize the file reading task.