Generally, it can be divided into the following categories: 1. Fixed bass variation: changing melody, texture, speed, dynamics, etc. 2, fixed melody variation: change harmony, tonality, texture, speed, intensity, etc. 3. Image variation (also known as decorative variation): changing rhythm, adding flowers to melody, changing speed, thickening or simplifying texture. 4. Variation of personality (also called free variation): expanding the theme, adding new materials to form contrast, changing the interval relationship and arrangement. 5. Variations on two or more themes