李衎尤善画枯木竹石，善画墨竹，双钩竹尤佳，和赵孟頫、高克恭并称为元初画竹三大家，著有《竹谱详录》，对于竹子的形态、性质、画法有详细的论述。
       墨竹初师金代王庭筠、王曼庆，后学文同，着色者师李颇，驰名当世。后来鲜于伯几建议他以色代墨写竹，既而学李颇、黄筌父子双钩设色法。他曾遍游东南山川林薮，后使交趾，深入竹乡，于竹之形色情状，辨析精到，是一位既具有深厚传统功力，又注意师法自然的画家。元代画竹的风气很盛行，但画竹的大类中也有许多细微的讲究，比如有专画双钩竹，青绿设色，细笔渲染；也有专画水墨竹，大笔渲染，有大写意的风度。李衎则是水墨竹画的代表人物，在画竹上创立了独特的风格，形神兼备，追求蕴籍、自然、象征人物品德高洁的内在美。李衎著有《竹谱》一书，是他生平画竹经验的总结，对不同地区各类竹的形色情状记述详细，对各类竹的各种画法也有详尽论述，是学习画竹者的津梁。
       李衎将竹视为“全德君子”，将尊竹之情融入了画中，赋予竹以生命，追求一种蕴籍、自然、象征人物品德高洁的内在美。李衎画竹高超的技艺在当时倍受人推崇，他尝奉诏画宫殿、寺院壁画。此外，李衎也间作勾勒青绿设色竹，还常写古木松石，由于他非常重视写实，高克恭曾评价李衎的画“似而不神”。其子李士行继承家学，传世作品有《乔松竹石图》轴等，画法出于乃父，唯功力稍差。作画竹、墨竹二谱。存世作品有《四清图》、《竹石大轴》、《沐雨图轴》，均藏故宫绘画馆。

《四清图》是李衎65 岁所画，用笔沉着稳健，墨色淋漓清润，将各种竹子的姿态及竹子的新老枯荣都表现得十分真切。此图约在明代中期被分为两段，前半卷现藏美国，画慈竹、笙竹二丛，上有赵孟、元复初题跋。图中所画兰、竹、石、梧名“四清”，意喻君子的高洁品性。画中枝叶虽密，但笔笔秀雅简洁，墨色浓淡相宜，变化自然。由于是卷装，梧桐和竹子多截取中段摄入画面，并采取了王庭筠《古木幽槎》构图方法，用笔沉着稳健，虚虚实实都被交待得清清楚楚，墨色淋漓清润，深浅浓淡被掌握得恰到好处，结构层次和空间处理得也十分恰当。整幅画面繁而不乱，疏密有致，给人一种身临竹前的感觉。 
       竹石图轴为元代李衎所绘，绢本，设色。纵185.5厘米，横153.7厘米。藏故宫博物院。该幅图未署名款，钤印两方，已残缺，可见“李”、“息”字。诗塘有明代李东阳的小草题记，也为此画增色不少。该幅“竹石图”是李衎的名作之一。图中竹以双勾填色而成，工整而有韵味，设色而又雅致，竹繁而不乱，表现了春天大自然中万物复苏、生机勃勃景色，有二杆新竹已与老竹并肩齐趋，让人联想到雨后春笋猛发的情景。坡上山石以细披麻皴画出，黑色沉重，以压阵角，石后穿插小竹野树，富有变化。

He is also known as the early bamboo painting three people, with the "bamboo spectrum recorded in detail," for the shape of bamboo, nature, painting a detailed description of the bamboo, bamboo, bamboo, bamboo, bamboo, .
       The beginning of the Jin Dynasty Wang Zhijun, Wang Manqing, after the study of the same text, the color division Li Po, well-known when the world. Later, in the United States to propose a few fresh ink to write bamboo, both learning Li Po, Huang Quan father and son set the color of the hook. He had traveled the southeastern mountains Lin Tau, after making toe, in-depth Zhuxiang, in the shape of the bamboo-like color, distinguish to the fine, is both a profound traditional skill, but also pay attention to the natural division of the painter. Yuan Dynasty painting bamboo atmosphere is very popular, but there are many small bamboo painting of the subtle stresses, such as a double-hook bamboo paintings, green color, fine pen rendering; also specializes in painting ink bamboo, large rendering, Of the grace. Li Biao is the representative figure of the ink and wash painting. He created a unique style in the painting bamboo, which is the inner beauty of noble character and noble character. Li Zhu, a book of "bamboo spectrum" is a summary of his life experience of painting bamboo, bamboo in different areas of various types of color and shape described in detail, the various types of bamboo have a detailed description of the painting is the study of bamboo Of the beam.
       Li Bamboo will be regarded as "the whole German gentleman," the bamboo into the picture of love, to bamboo to life, the pursuit of a Yunji, natural, symbolic character of the inner beauty of noble. Li Zhu painting superb artistry at the time much respected, he tasted Feng Zhao palace, temple murals. In addition, Li is also an interlude between the outline of green color bamboo, but also often write ancient wood turquoise, because he attaches great importance to realism, Gao Ke Gong Li has evaluated the painting "like God". His son Li Shixing inherited family learning, handed down works of "Qiaosong bamboo stone" axis, painting for the father, only slightly less skill. Painting bamboo, bamboo two spectrum. Surviving works are "four clear map", "Bamboo Shaft", "Muyu axis", are possession of the National Palace Museum.