Traditional evaluation methods of learning do not recognize cognative changes in the learners. They only compare the scores of the pre and post learning tests. In this study, we have tried to evalute the environmental education program the aim of which is to change the learners' cognition about their environment. Accordingly we have developed the Hierarchical Graph Method to provide a new evalution technic to measure the change of the learners' cognition between the pre and post learning tests. This was based on biliometric methods. The Hierarchical Graph Method analysis the data on the free answers to the pre and post tests. As a result we can show the process of cognitive change of learners by a graph. In conclusion we judge that the Hierarchical Graph Method could become a good method to measure the change of learners' cognition or knowledge.