Abstract: The way of “writing” (写) is one of the characteristics of pen-and-ink expression in Chinese literati painting, which is prominently embodied in the aesthetic ideology and the paintings of the Yuan dynasty painter Ni Zan. Ni Zan’s principle and practice of “writing” painting is rooted both in his inheritance of the pen-and-ink traditions of the Song and Yuan literati painters and in the following concepts in the history of painting: “a common origin for Chinese painting and calligraphy,” (书画同源), “a common essence for Chinese painting and calligraphy,” (书画同体) and “a common method for Chinese painting and calligraphy” (书画同法). In Ni Zan’s paintings, he used calligraphic brushwork to capture the romantic charm of the objects, which was a free expression of his true feelings and a means of self-entertainment. At the same time, his painting and calligraphy were influenced by the social trend emphasizing the “integration of literature and art” (文艺相融) in the Yuan Dynasty, resulting in a high degree of internal consistency among pen-and-ink performance, creative approaches and aesthetic style. Consequently, there was a certain degree of inevitability to the introduction of a “writing” style into his paintings. Ni Zan’s calligraphy and painting are intertwined and integrated, presenting the visual characteristics of the same brushwork. The principle of blank space is similar in both calligraphy and painting, and the same common principles apply to ink intensity and a carefree style. More importantly, “writing” (写) in his paintings, as a way of conveying the language of Ni Zan’s pen-and-ink style, also embodies the character of high elegance, which made the pursuit of a written mood in pen-and-ink paintings a common goal of literati paintings throughout the Ming and Qing dynasties.