杜甫題畫詩有二十九首，與書法有關之詩作亦達二十多首，不但可以見其人格性情，亦可以推知其美學理論。
論書主張:
一、論紹統:入古而出古。書法須有所淵源、能兼通數家、能入古而又出古，既能紹統，又能求變。
二、論筆力:瘦硬見其力。詩中常以軍器、劍器、銀鉤喻書法之線條的力度，以龍蛇、蟲蛇等其象之詞喻其線條之瘦，所謂「書貴瘦硬方通神」。
三、論氣韻:無可尋之跡。筆墨相發，則氣韻自現，詩中以動態之物象徵，如「驚聳立」、「鳳霧騰」之無跡可尋，形成於有意無意之間。
論畫主張:
一、論形神:度象取真、形神備其。常以觀畫恍若身臨其境讚美畫作之逼真。二、論價值:藝術無價、不可實度。讚美畫中假物的藝術價值超過真物。
三、論欣賞:意翻題外、延伸意趣。觀畫往往找尋出畫外別首，而成為題畫詩中最扣人心弦的部分。
四、論創作:虛實相生、道通心神。創作的態度應該從容不迫，才能產生佳作。創作必須心無旁驚，方能心與神融。
由杜甫論書與論畫詩可推其美學主張:
一、聯想是文學藝術的會通。即論詩與書畫原創作品之會通。美感經驗中，從書畫作品看到了意象，而這些意象傳出一種特殊的情趣，這就是審美的過程。
二、氣韻是書畫美學的共象。論書法最重要的語句莫如「書貴瘦硬方通神」，論繪畫最重要之句莫如「元氣淋漓障猶濕」，二句均寫出了書畫所追求的最高境界一一氣韻。

Totally there are 29 poems about painting and more than 20 poems about Calligraphy written by Du Fu. From those poems， not only his characteristics and personalities are manifested， but his own viewpoints and theories of Aesthetic.
Du Fu's views on calligraphy:
A.As to the characters in a calligraphy work， Du Fu advocates that the style of characters has to inherit the tradition， which should be juxtaposed with the establishment of a distinguished self-style. In other word， it should abide by its origin and blend the characteristics of different calligraphers to have more innovation.
B.As to the vigor of strokes in calligraphy writing， slenderness and firmness display the strength in a work. Weapons， swords， and sliver clasps are similes applied in poems to depict the strength of each stroke; dragons and snakes are concrete metaphors to illustrate the slenderness of every line in calligraphy. That is to s呵， it is the slenderness and firmness that reveal the exuberance of calligraphy.
C. As to temperament and aroma of calligraphy， there are no tracks to follow. They will be spontaneously overflowing during the interaction between brushes and ink. In poems， animated images are used to symbolize this nature， such as "a luan (a mythical bird in Chinese legends) rises straight" and "a phoenix flies high"， which leave no prints to trace. The temperament and aroma of calligraphy are always created unwittingly， while nothing can be originated if done intentionally.
Du Fu's views on painting:
A.As to the external form and internal spirit in paintings， Du Fu states that both features should be equipped; the inner spirit in a painting can be revealed from its externals， which can make a viewer feel the reality of the setting in a painting in person.
B.Asto the value in paintings， it is beyond price and cannot use any mundane standards to evaluate.
C. As to the appreciation in paintings， Du Fu argues the artistic conception in a painting usually overpasses the painting topic presented externally. The theme beyond the painting that a painter wants to express is the most soul-stirring and touching part in the poems about painting.

D. As to the artistic creation in paintings， the unspoken fictitious state of mind is usually mixed with the factual formality in paintings. The artistic conception presented by the painter is internally linked with his spirit. A painter who is competent to create masterpieces should be calm and quiet. He should keep the concentration， so his soul and temper can blend with the spirit in paintings.

The Inference ofDu Fu's aesthetic observation from his poems about calligraphy and paintings:

A.Through differed types of literature and art， imagination in a work is comprehensible. That is， the imagination between the commentary poems about calligraphy or paintings and the original work is interlinked. The process to appreciate beauty is through your experiencing of aesthetic， the acquiring of images from calligraphy and paintings， which serve the viewers the delighted interest and appeal.
B.Temperament and aroma are the common presentations of beauty in calligraphy and paintings.
One of the important quotations of the commentary of calligraphy as“The value of calligraphy lies in its strength and slenderness， which leads to the supernatural spirit."， and “Thevividness and limpidity of the painting lively refresh you with image of flowing mist."， which is a comment on paintings， emphasize the highest standard on calligraphy and paintings， and that is， the artistic conception and temperament.