I the tip of the tongue gently touches the lower teeth, not between the upper and lower teeth, but inside the lower teeth. Smile at your mouth, pronounce it, and feel an air flow through the small gap between (upper teeth) and (lower tongue), and flow out without hindrance.

I is the vowel phoneme of Chinese pinyin, also called vowel, which can be its own syllable. According to the naming principle of vowels, the professional name of I is "vowel with high and round front lip", which represents the standard tongue position and lip shape when pronouncing.

When there is no vowel before the vowel in the I-train, it is written as yi (meaning), ya (elegance), ye (leaf), yao (you), yan (smoke), yin (cause), yang (yang) and ying (English).

A (ah) has a wide mouth, the lowest tongue position and a slightly upturned back.

O (Oh) has a round mouth, a slightly backward tongue, and a slightly upturned back (pronounced O, not ao or ou, see the note below for details).

E (Goose) has a flat mouth, and its tongue position is roughly the same as that of O, except that its mouth is spread to both sides.

I (clothing) teeth are arranged neatly, and the mouth shape is flat. The tip of the tongue touches the back of the lower teeth, making the front of the tongue convex.

U has a pointed mouth, a round lip, a small hole and a backward tongue.

The pronunciation of "Yu" is basically the same as that of "I" except that the lips are round and slightly protrude forward, and the tip of the tongue rests on the back of the lower teeth.