Don't confuse this book with Yao Zui's 姚最 book Xu huapin 續畫品.
The Xu huapin 續畫品錄 "Continued classification of painters" is a critique on painters attributed to the Tang period 唐 (618-907) scholar Li Sizhen 李嗣真 (?-696), courtesy name Li Chengzhou 李承胄, who came from Zhaozhou 趙州 (modern Xiping 西平, Henan) or Huazhou 滑州 (modern Changyuan 長垣, Henan) and was palace aide to the Censor-in-chief (yushi zhongcheng 御史中丞). He was later demoted and exiled to southern China where he died.
Li Sizhen was known as an expert in music and astronomical calculation, but also for his paintings of Buddhist and Daoist deities. He had been a disciple of the painter Yin Lin 尹琳, who was also the teacher of Li Zhongchang 李仲昌. Li Sizhen is also mentioned in the painting critique Tangchao minghua lu 唐朝名畫錄, yet neither his strengths and shortcomings are described, nor is he ranked by his quality.
Li Sizhen's abilities and works are at least mentioned in Zhang Yanyuan's 張彥遠 Lidai minghua ji and the bibliography Junzhai dushu zhi 郡齋讀書志, but in another context, so that a lot of scholars doubt that he was the author of the Xu huapin lu. The content of Li Sizhen's book is also very similar to that of Yao Zui's 姚最 book with the title Xu huapin 續畫品 or Xu huapin lu, but the latter is not mentioned in a single word. It might be that Li's book was lost at an early point of time, and later collectors tried reconstructing the book by copying sentences from Yao Zui's book. Zhang Yanyuan's Fashu yaolu 法書要錄 lists another book by Li Sizhen, the short text Hou shupin 後書品, which is a critique of 81 calligraphers that are classified in ten ranks. This book is structured very clearly, and the lost book Xu huapin lu might have had a similar style of composition, very unlike the received Xu huapin lu, which is course and confuse.
Li Sizhen's Xu huapin lu is included in the collectanea Jindai mishu 津逮秘書, Wangshi shuhua yuan 王氏書畫苑 and Zhongguo hualun leibian 中國畫論類編.
Source: Li Xueqin 李學勤, Lü Wenyu 呂文鬰 (1996). Siku da cidian 四庫大辭典, vol. 2, p. 1798. Changchun: Jilin daxue chubanshe.