本文討論《左傳》、《國語》所載「中大夫」之含義及職司內容，認為「中大夫」不可與「上大夫」、「下大夫」排比，視為「大夫」等第。《左傳》所載「大夫」一詞前常冠以其他名詞，如「中軍大夫」、「上軍大夫」、「下軍大夫」、「七輿大夫」、「公族大夫」及「僕大夫」。筆者認為，冠諸「大夫」前名詞即是該大夫職司範圍。依此詞例，則「中大夫」職司範圍即為「中」。「中」即「內宮」，是國君內廷；「中大夫」為管理「中」之大夫，即掌理國君內廷之大夫。「中大夫」於《左傳》、《國語》僅出現三條記載，且集中於晉獻公、惠公時期，此時擔任「中大夫」之里克、丕鄭等同於「卿」。自西周以來，內廷官如「宰」、「膳夫」已由原本掌理周天子內廷進一步掌握權勢，躍居朝堂要津。晉獻公時期「中大夫」里克、丕鄭如西周「宰」、「膳夫」之例，由原本掌理國君內廷，進而掌握晉國「卿」之實權。晉國「作三軍」後，「卿」由三軍將佐取代，此後「中大夫」極可能回歸原本職司。由於重要性已然不再，故而此後便不見「中大夫」記載於《左傳》及《國語》。

This paper focused on the duty of ＂Zhong Dai Du＂ documented in ＂Zuo Zhuan＂ and ＂Guo Yu＂. I proposed that we should not regard ＂Zhong Dai Fu＂, ＂Shang Dai Fu＂ and ＂Xia Dai Fu＂ as different social rank. On the contrary, in the earlier literature before ＂Zuo Zhuan＂, ＂Dai Fu＂ often came with other descriptions, such as ＂Zhong Jun Dai Fu＂, ＂Shang Jun Dai Fu＂, ＂Xia Jun Dai Fu＂, ＂Qi Yu Dai Fu＂, ＂Gong Zu Dai Fu＂, and ＂Pu Dai Fu＂. As a consequence, I argued that all the descriptions before ＂Dai Fu＂ should be considered their duty. In other words, the duty of ＂Zhong Dai Fu＂ should be ＂Zhong＂. In the literature, ＂Zhong＂ referred to the palace, or the imperial residence. That is, ＂Zhong Dai Fu＂ was responsible for managing the imperial residence. In ＂Zuo Zhuan＂ and ＂Guo Yu＂, ＂Zhong Dai Fu＂ was only mentioned three times in the period of Duke Xian of Jin and Duke Hui of Jin. During the time of the two Dukes, Li Ke and Pi Zheng served as ＂Zhong Dai Fu＂, and had several campaigns under their command. As a result, we could infer that ＂Zhong Dai Fu＂ Li Ke and Pi Zheng's duty are the same as ＂Qing＂. Since Western Zhou, the officers in charge of the imperial residence such as ＂Zai＂ and ＂Shan Fu ＂ had seized the power not only over the palace affairs but also over the national issues. This paper argued that the ＂Zhong Dai Fu＂ Li Ke in the period of Duke Xian of Jin was exactly the same as ＂Zai＂ and ＂Shan Fu ＂ in Wester Zhou, originally in charge of the imperial residence affairs but ended up as grabbing the power like ＂Qing＂, commanding the troops to have several campaigns. After the movement of ＂Zuo San Jun＂, the position of＂Qing＂ was replaced by the troops commander. Due to this reason, the power of ＂Zhong Dai Fu＂ was limited to the imperial residence affairs, and the importance of which may thus be decreased. Therefore, it would not be dated in ＂Zuo Zhuan＂ and ＂Guo Yu＂.