Thinking about the interactions among geographical elements, referred to here as geographical interrelationships thinking, is a crucial part of geographical synthetic thinking. Causal diagrams are commonly employed in geography to cultivate students' geographical synthetic thinking. To test the hypothesis that teaching with geographical causal diagrams can enhance students' geographical interrelationships thinking, the author designed a teaching experiment. A total of 37 high school students participated in the one-month four-lesson teaching experiment. The results showed a significant improvement in students' geographical interrelationships thinking. There was a significant positive correlation between students' proficiency in drawing causal diagrams and their geographical interrelationships thinking.