Yu Jin 于禁 (d. 221), courtesy name Wenze 文則, was a general of the warlord Cao Cao 曹操 during the last decades of the Eastern Han period 東漢 (25-220 CE).
He hailed from Juping 巨平 in the commandery of Taishan 泰山 (today's Tai'an 泰安, Shandong) and participated in Bao Xin's 鮑信 suppression campaign against the Yellow Turban rebellion 黃巾起義. Later on he became a follower of Cao Cao, who made him commandant of cavalry (sima 司馬) and commander subduing the phalanx (xianzhen duwei 陷陣都尉). Yu Jin participated in the war against Lü Bu 呂布, Zhang Xiu 張繡 and the tyrant Yuan Shao 袁紹. For his military successes he was given the titles of General to the Left (zuo jiangjun 左將軍) and was given the title of Neighbourhood Marquis of Yishou 益壽亭侯. For his military success against Chang Xi 昌豨, Yu Jin was given the title of General with the Authority of a Tiger (huwei jiangjun 虎威將軍).
In 219, he asked to be sent to Fancheng 樊城 to support Cao Ren 曹仁 against Guan Yu 關羽. Unfortunately heavy rain swelled the waters of River Han 漢水, and many troops of Yu Jin's army drowned, so he had to surrender to Guan Yu. Yet when the southeastern warlord Sun Quan 孫權 conquered the province of Jingzhou 荊州 (central China), Guan Yu and all his officers were captured and taken prisoners in Wu 吳 (222-280), the realm of Sun Quan.
In 220, Cao Cao's son Cao Pi 曹丕 (known as Emperor Wen 魏文帝, r. 220-226) adopted the title of Emperor of Wei 曹魏 (220-265), and nominally Sun Quan accepted his overlordship, and sent back Yu Jin. Emperor Wen pardoned Yu Jin and gave him the title of General of Widespread Pacification (anyuan jiangjun 安遠將軍), yet for the tomb of his father, Cao Pi had a painting produced showing the defeat of Yu Jin by Guan Yu. Feeling ashamed, Yu Jin soon died.