李懷民在《重訂中晚唐詩主客圖》選本中，透過選詩與評論，建構出以「水部家法」與「賈師法門」為標準的五言律詩典範。首先，李懷民倡導「學詩由五律始」，批評明代以來喜作七律而淪於膚廓的弊病；同時強調張籍、賈島五律在中晚唐詩的重要影響。李懷民所建立的「水部家法」與「賈師法門」，是從歸納張籍、賈島以及其後學者們五言律詩作品而來，與傳統直觀印象的批評方式有所不同。其次，重視詩歌題目的制定，提出特定體例的置題法，以及強調詩題與詩作主題、情感表達之間的呼應。第三，聚焦於五律篇章的結構，從首聯的起，到中間兩聯的對仗，再到尾聯的結，李懷民都提出獨到深刻的觀點，強調平淡見深情、平常語見奇幻的表現特色。在清代前期推尊盛唐、杜甫為主的風氣中，李懷民獨標由中晚入盛唐的詩學觀，透過《重訂中晚唐詩主客圖》一書，建立以張籍、賈島為主的五言律典範。

Li Huai-min discussed and criticized the five-syllable Lines and verses of in the Middle and Late Tang Dynasty. He not only rediscovered the importance of the poetry of the middle and late Tang Dynasty, but also constructed a evaluation standard of five-syllable Lines. First of all, he emphasized that the five-syllable Lines is an important beginning of learning poetry. Secondly, Li Huai-min He believed that the title of a poem determines the quality of the work. Thirdly, He specifically pointed out the structure of five-character verses. As a result, Li Huai-min demonstrates Zhang and Jia’s poems as two different trends of poetry and indicated the relationship between them based on their artistic characteristics.