Yu Kaifu: It refers to Yu Xin. In the Northern Zhou Dynasty, from the official to the general of a title of generals in ancient times and the third division of Kaifu instrument (Sima, Situ and Sikong), it was called Kaifu in history.
Elegance: a kind of "heroic". Bao Shen Jun: Bao Zhao. The former army of Jingzhou in the Southern Song Dynasty joined the army, and the world called Bao joined the army. On Du Fu's Memories of Li Bai's Spring in Tang Dynasty
The first sentence praised his poems as the best in the contemporary era. This sentence is an explanation of the previous sentence, which means that the reason why he "has a way in his poem" lies in his ideological interest and extraordinary features, so his poems are unparalleled.
Then praise Li Bai's poems as fresh as Yuxin and elegant as Bao Zhao. Yu Xin and Bao Zhao were both famous poets in the Southern and Northern Dynasties. These two sentences are forceful and full of enthusiasm. From the frank and sincere praise of this poem, we can also see that Du Fu highly praised Li Bai's poems.
Extended data
Creation background of the poem: This poem was written by Du Fu when he lived in Chang 'an in the spring of Tianbao (746) or Tianbao (747) in Xuanzong of Tang Dynasty. In 744 AD (Tianbao three years), Li Bai and Du Fu met in Luoyang, and the latter two went to Songzhou together, where they met the poet Gao Shi in Wenshui, north of their single father (now south of Shanxian County, Shandong Province). Later, we went to Daliangcheng together.
After breaking up, Li Bai rushed to Jiangdong and Du Fu went to Chang 'an. It is natural that the whole poem begins with a poem and ends with "paper", from poem to person, from person to poem, and turns around. The word "memory" runs through the whole poem, blending the admiration and nostalgia for people and poetry. The lyrical technique of scenery is even more superb, and the author's feelings of missing are deeply written.
References:
Baidu Encyclopedia-Remembering Li Bai in Spring