Heavenly stems and earthly branches is a collective name of ten trunk branches and twelve branches, commonly known as ten trunk branches and twelve earthly branches, and referred to as trunk branches for short.

Originated from China's observation of celestial phenomena in ancient times. The simplified heavenly stems and earthly branches: "A, B, C, D, E, Ji, G, Xin, Ren, Gui" is called the ten heavenly stems, and "Zi, Ugly, Yin, Mao, Chen, Si, Wu, Wei, Shen, You, Xu, Hai" is called the twelve earthly branches.

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1, used for calendar and time: heavenly stems and earthly branches was mainly used for calendar year, month, day and time in ancient China.

2. Used for ordinal number, rating and classification: After the main ordinal number function of heavenly stems and earthly branches has been replaced by the first, second, third and fourth digits, people still use them as general ordinal numbers. Especially, A, B, C and D can be used not only to list classified articles, but also to rate and classify things in daily life.

3. It is used in Confucianism, Neo-Confucianism, medicine, geomantic omen, astrology and numerology: in the theory of Yin-Yang and Five Elements, branches and branches are divided into Yin and Yang according to their order, and every odd number belongs to Yang, and every even number belongs to Yin. A, C, E, G, and N in heavenly stems, and children, Yin, Chen, noon, Shen, and Xu in earthly branches are yang numbers; The heavenly stems of B, D, Ji, Xin and Gui, and the earthly branches of Ugly, Mao, Si, Wei, Unitary and Hai are negative numbers. On this basis, according to the theory of mutual restraint, the harmony, rise and fall, conflict and its birth and death of personnel are calculated.