Abstract: This article explores how polysemy of words in the temperature domain is extended through the temperature image schema and the conceptual metaphors based on it from the cognitive linguistic perspective. Our study indicates that in the temperature image schema, the degrees of temperature and their changes are constructed in terms of the vertical spatial concepts of UP and DOWN. Based on this image schema and through metaphorical mappings, there forms a conceptual metaphor system in English—the Temperature Metaphor System that consists of three-layered metaphorical mappings, i.e., THE STATE OF THINGS IS TEMPERATURE, THE DEGREES OF THE INTENSITY OF THE STATES OF THINGS ARE THE DEGREES OF TEMPERATURE, and THE CHANGES OF THE STATES OF THINGS ARE THE CHANGES OF TEMPERATURE. As a cognitive mechanism, this metaphor system gives rise to numerous non-temperature concepts and forms a unique inference pattern. It constrains our interpretation and use of the entrenched temperature metaphorical concepts and linguistic expressions on the one hand and enables us to create novel concepts and linguistic expressions on the other.