He hailed from Donghai 東海 (modern Cangshan 蒼山, Shandong) and was an expert in the new-text (modern characters) classic Yijing "Book of Changes" and was the founder of the Meng school (Mengshixue 孟氏學) of the Yijing.
His father Meng Qing 孟卿 already excelled in the ritual classics and the Chunqiu 春秋 "Spring and Autumn Annals" that he had studied by Hou Cang 后蒼 and Shu Guang 疏廣. Yet he believed that the ritual classics were too complex and the Chunqiu too confuse and so had his son study the Yijing by Tian He 田何 and his brother Tian Wangsun 田王孫.
Meng Xi's most important colleagues were Shi Chou 施讎 and Liangqiu He 梁丘賀. The relations between teacher and student were quite uncommon among this group, and less hierarchic than normally. Meng Xi therefore was never appointed erudite (boshi 博士) and had to be content with posts like that of court gentleman (lang 郎) or office chief (shuzhang 署長).
Meng Xi's Yijing explained the weather by the 64 hexagrams and prognosticated fortune and mischief. Together with Jing Fang's 京房 explanation of the Yijing, this Confucian Classics became very popular during the Han period.
Meng's book Zhouyi Mengshi zhangju 周易孟氏章 was lost at an early point of time, yet some surviving fragments were collected by the Qing period 清 (1644-1911) scholar Ma Guohan 馬國翰 in his Yuhan shanfang jiyi shu 玉函山房輯佚書, as well as by Huang Shi 黃奭 (Hanxuetang congshu 漢學堂叢書) and Sun Tang 孫堂 (Han-Wei shiyijia Yi zhu 漢魏二十一家易注). Meng Xi was also rediscovered by the Qing period philosopher Hui Dong 惠棟 in his Yi Han xue 易漢學 "Studies to the Yijing teachings of the Han period".