Abstract: Continuity equation is an important basic equation in fluid mechanics. In the teaching process, it is often focused on the application in engineering, the basic concepts and physical significance are ignored. This paper presents a systematic teaching method, which integrates the basic concepts of continuity equation in series. Reynolds transport theorem is applied to different flow models to derive four different forms of continuity equations to prove that they can be transformed into each other and are essentially the same equation. This teaching method helps students to deepen their understanding of the physical meaning of the basic formulas of fluid dynamics and builds a basic idea for the study of fluid mechanics.