Yi Ma Xing (Post Horse Star) is one of the Shen Sha (Divine Stars and Malevolent Influences) in Bazi astrology, signifying travel, relocation, and movement. Yi Ma Xing is determined by the Year Branch or Day Branch: for the Earthly Branch combinations Yin-Wu-Xu, the Post Horse is Shen; for Si-You-Chou, it is Hai; for Shen-Zi-Chen, it is Yin; and for Hai-Mao-Wei, it is Si. Individuals with Yi Ma Xing in their chart tend to experience frequent travel and relocation throughout life, making them well-suited for professions involving business trips, tourism, or transportation—yet they also tend toward instability.
Determine Yi Ma Xing based on the Year Branch or Day Branch: for years/days falling under Yin-Wu-Xu, Shen is the Post Horse; for Si-You-Chou, Hai is the Post Horse; for Shen-Zi-Chen, Yin is the Post Horse; for Hai-Mao-Wei, Si is the Post Horse.
A person born in the Year of Yin (Tiger) whose Four Pillars contain the Earthly Branch Shen (Monkey) has Yi Ma Xing present in their chart, indicating a life marked by frequent travel and relocation.