It is better to say the surname+principal, or omit the surname and call the principal directly. There are two reasons: first, people nowadays are more fashionable in their professional titles; Secondly, according to China's address tradition, surname+teacher is impolite, but surname+position is feasible.

The traditional name of China is:

Surname (clan surname): surname must be extremely respectful, such as a certain public, an certain Weng, a certain virtue, an official, etc. (and it is usually used when preaching or quoting others, and it is rarely used to address people face to face).

Name: It can be used to address people, but it is not commonly used. Few people call them by their first names.

Word: (used to explain or extend the meaning of "name", such as: name Zedong, word Runzhi; The name is in the middle and the word is stone).

Number (different times and different realms can have different numbers).

Words and numbers are appellations in daily life, which can be addressed directly or followed by honorifics.

If it is necessary to use full names by name, such as letters, the format should be: add a respectful name after the last name, and indicate the relationship or seniority after the first name or word. Instead of writing the last name with the first name and the word. For example:

Dear brother Mao (space) runs (space);

Zhang Dade (blank), big brother Daqian (blank), Dao Qi;

President Jiang (blank) Mr. Jieshi is sincere;