Abstract: Bloch equation is one of the most important equation for understanding Nuclear Magnetic Resonance （NMR） based on classical mechanics. It is necessary for students to catch it as the fundamentals of NMR. Annotations on the form of Bloch equation and solving Bloch equation by stages are made, in order to supplement the lack of the details knowledge in the related textbooks and help students in doing NMR experiment.

Key words: Bloch equation, Nuclear Magnetic Resonance, relaxation