OBJECTIVE: The association of spleen system including both spleen and stomach with earth, one of the five elements, is a part of the theory of five elements. Practitioners of Traditional Chinese Medicine (TCM) used the theory as a reasoning tool to illustrate the Zang-Fu organs' physiological functions and the interaction among them.The exploration of how the theory of that spleen system is associated with earth was created may provide insights into how five-element theory is applied to TCM practice. METHODS: Using analogism as a method to explore the relationship between earth and spleen system inTCM. RESULTS: Chinese ancestors experienced and observed the features of earth from agricultural practice and used the knowledge for the explanation ofspleen system functions including physiological functions, pathological characteristics and for the treatment of related illnesses. CONCLUSION: The theory of the five elements in TCM is a kind of metaphor, which depends on observation and exploration of the natural world and experience of human beings.