In the history of Chinese poetic criticism, Du Fu's (712-770) penta-syllabic quatrains have been praised and criticized. This phenomenon reflects the diverse aesthetic standards and views of the representation functions of quatrains in the scholarship of Du Fu. If we focus only on penta-syllabic quatrains and trace the conventions of this poetic form according to its theory of representation, we may find among the 30-plus poems penned by Du some that meet the traditional aesthetic standards of penta-syllabic quatrains and some "innovative tunes" in the respects of theme, structure, and artful representation. This innovation is especially evident in scenic depiction, which saw a breakthrough from the traditional formula of representation in penta-syllabic quatrains. It also explored a deeper level of aesthetic feelings and thereby opened up for later generations new exploration in the genre's potential of representation. Therefore, the significance of Du's experiment must not be underestimated.