Xu shuduan 續書斷 is a book on the critique of calligraphy. It is actually part (ch. 9, 12) of Zhu Changwen's 朱長文 (1039-1098) book Mochibian 墨池編, but was also dealt with separately and is found in the series Siku quanshu 四庫全書, Shugu congchao 述古叢鈔, Yishu congshu 藝術叢書 and Cangxiutang congshu 藏修堂叢書.
The book of 2 juan length imitates Zhang Huaihuan's 張懷瓘 (early 8th cent.) calligraphy critique Shuduan 書斷 and add information missing in Zhang's original. Zhu discusses painters of the late Tang 唐 (618-907) and the early Song period 宋 (960-1279) according to three categories, namely "inspired" (shen 神), "excellent" (miao 妙), and "competent" (neng 能) and explains the strengths and shortcomings of each calligrapher in detail. He identifies three "inspired" masters, namely Yan Zhenqing 顔真卿 (709-785), Zhang Changshi 張長史 (early 8th cent.), and Li Yangbing 李陽冰 (early 8th cent.), 16 "excellent" masters, and 66 (64) "competent" masters. For about a dozen contemporary artists, Zhu Changwen does not provide a grade of mastery (ch. Xishuo 系説). The book also includes short biographies of 33 persons.