Mozart Piano Sonata Nr281 (K.547) is a classic piano work with a complex and rigorous musical form structure. The following is an analysis of the musical form of this work:

1. Presentation (bars 1-40):

Main theme (bars 1-8): Begins in B flat major , the melody is soft and beautiful, with typical Mozart style.

Connecting part (measures 9-17): Based on the main theme, through changes in harmony and melody, it pave the way for the emergence of the secondary theme.

Secondary theme (bars 18-30): Appears in the key of F major. The melody is fresh and bright, contrasting with the main theme.

Ending part (measures 31-40): Based on the theme of the secondary part, through a series of changes in harmony and melody, preparations are made for the expansion part.

2. Expansion (sections 41-69):

Introduction (sections 41-44): Based on the main theme, the expansion is introduced through changes in harmony and melody. The main content of the department.

Expansion of the main material (measures 45-61): Based on the melody and harmony of the main theme, the music is made richer and more complex through a series of changes and developments.

Preparation for Dominant Continuing Sound (measures 61-67): Based on the material of the secondary theme, prepare for the emergence of dominant chords through the use of Dominant Continuing Sound.

Dominant chords (measures 68-69): Based on dominant chords, prepare for the recapitulation through harmonic changes.

3. Reappearance (bars 70-109):

Reappearance of the main part (bars 70-77): Based on B flat major, reproduce the melody and harmony of the main theme sound, making the music more complete and unified.

Connecting part (bars 78-86): Based on the theme of the main part, through changes in harmony and melody, preparations are made for the reappearance of the secondary part.

Reproduction of the secondary part (measures 87-99): Based on the key of B flat major, the melody and harmony of the secondary part theme are reproduced, making the music more complete and unified.

Ending part (bars 100-109): Based on the theme of the secondary part, through a series of changes in harmony and melody, the music gradually calms down, and ends with the melody of the main part, making the music complete And harmonious.

To sum up, the musical form structure of Mozart Piano Sonata Nr281 is rigorous and complex. Through the theme contrast in the presentation part, the material development and continuous tone preparation in the development part, and the reproduction and unification of the recapitulation part, It shows the unique charm and perfect performance of Mozart's music style.