The theory of music education is a theory specifically aimed at the learning and teaching process of music education. It covers all aspects of music, ranging from its basic elements, such as rhythm, melody, and harmony, to musical psychology and social dynamics, and how to teach music effectively. Music theory plays a key role in understanding and evaluating the various aspects of music education. These theories not only provide the basis for the understanding and interpretation of music education, but also provide the guidance for how to teach effectively. In this paper, the application of music education theory in piano teaching and the relationship between music education theory and children's physical and mental development, so as to show the importance of music teaching theory.