"C programming language" is a practical course for teachers and students, and this course is difficult to teach or learn. This paper applies the case of the "water lamp circuit" into all the chapters throughout the C language teaching in. The "water lamp circuit" in the teaching process of the organization and implementation has been analyzed in detail to make students be familiar with the grammar, grasp the statement in the process of solving practical problems, and greatly stimulate students' interest in learning, which also improves the teaching efficiency.