Syllable is the fundamentally structural unit in speech sound and also the smallest phonetic unit that people can catch spontaneously. The syllable in putonghua usually comprises of three parts: Shengmu, Yunmu and Intonation. Generally speaking, the pronunciation of a Chinese character is a syllable. It is made of 1 to 4 phonemes. Shengmu is the beginning of a syllable. There are 22 shengmu in putonghua including 21 consonants and 1 lingshengmu (zero initial consonant). Behind shengmu in a syllable, there is yunmu, which is mainly made of vowels. In the total 39 yunmu in putonghua, there are 23 pure vowels and 16 compound vowels with terminal nasal consonants.

Shengmu may be classified into 7 types according to the pronunciation position: (1) 3 Bilabials (b, m, p); (2) 1 Labiodental (f); (3) 3 Front tongue tips (z, c, s); (4) 4 Middle tongue tips (d, t, n, l); (5) 4 Rear tongue tips (Palato-Alveolar) (zh, ch, sh, r); (6) 3 Front tongue surfaces (j, q, x); (7) 3 Rear tongue surfaces (g, k, h)

Shengmu may also be classified into 5 types according to the pronunciation methods: (1) 6 Oral stops (Plosive) (b, p, d, t, g, k); (2) 3 Nasals (m, n, ng, in which "m"and "n" are used as shengmu); (3) 6 Fricatives (f, h, x, sh, s, r); (4) 1 Lateral (l); (5) 6 Affricates (j, q, zh, ch, z, c)

Shengmu may be divided into two types, Voiceless sound and Voiced sound based on whether the articulation causes vibration. Except for the voiced sound m, n, l and r, all the shengmu in putonghua are voiceless sound.

In addition, shengmu may also be divided into two types, Aspirated sound and Unaspirated stop in terms of the powerfulness of air-stream. Aspirated sound and Unaspirated stop appear in pairs, such as b and p, t and d, g and k, z and c, zh and ch as well as j and q.

Every syllable of Chinese characters has two parts of shengmu and yunmu, and the pronunciation of each character includes shengmu, yunmu and intonation. Normally, lingshengmu refers to a syllable without the consonant shengmu, for example, "安" (ān), with the vowel "a" but not a consonant as its beginning. Such syllable is called lingshengmu.

There are 39 yunmu in Putonghua, of which 23 are pure vowels and 16 are compound vowels with terminal nasal consonants. Considering the different structures of yunmu, we classify it into three categories, i.e. single yunmu, compound yunmu and nasal yunmu.

The first category is single yunmu. There are 10 single yunmu in Putonghua, 7 of which are single vowels of tongue surface, i.e. a, o, e, ê, i, u and ü; and 3 are special single yunmu, i.e. -i (front), -i (back) and er.

The second category is compound yunmu that constitutes of several vowel elements and sound like a fixed vowel group. There are 13 compound yunmu in Putonghua. According to the position of the main vowel, compound yunmu are classified into front sound, back sound and intermediate sound compound yunmu. The front sound compound yunmu have the main vowel in front, including ai, ei, ao and ou. The back sound compound yunmu have the main vowel at the back, including ia, ie, ua, uo and üe. And the intermediate sound compound yunmu have the main vowel in the middle and include iao, iou, uai and uei.

The third category is nasal yunmu with n or ng as the yunwei (terminal consonant in a compound yunmu). There are 16 nasal yunmu of two types in Putonghua. One type is called front nasal Yunmu with nasal apical n and it includes an, ian, uan, üan, en, in, uen and ün; another type is called back nasal yunmu with nasal velar ng and it includes ang, iang, uang, eng, ing, ueng, ong and iong.

A yunmu includes yuntou (head vowel), yunfu (essential vowel) and yunwei (tail vowel). For example, the yunmu iao has i as its yuntou, a as its yunfu and o as its yunwei. Yunfu is the main part of a yunmu and sounds loudest with the mouth open wider. However, not every yunmu has all of the three parts of yuntou, yunfu and yunwei. Some yunmu have only yuntou and yunfu, such as ia, uo and üe, in which i, u and ü are their yuntou and a, o and ê are their yunfu; some have only yunfu and yunwei, such as ai, ei, ao and en, in which a, e, a and e are their yunfu and the vowels behind the yunfu are yunwei. Single yunmu have only yunfu without yuntou and yunwei. There are only 3 yuntou (i, u, ü) and 4 yunwei [i, u (include o in ao and iao), n, ng] in the yunmu of Putonghua. Yunfu is indispensable in a yunmu.