快速答案
demais 连写，可作副词、代词或形容词；当 de 属于周围句法结构时，de mais 分写。
可靠的方法是先判断这个词在句子里的功能，再翻译。
每个词的作用
demais
too much, very, or the others
Use demais for excessive degree, strong intensity, or the remaining people and things.
de mais
more than expected or of more
Use de mais for a prepositional combination opposed to de menos or used after certain nouns and pronouns.
如何选择
- demais: Choose demais if the sentence points to excessive degree, strong intensity, or the remaining people and things.
- de mais: Choose de mais if the sentence points to a prepositional combination opposed to de menos or used after certain nouns and pronouns.
例句
A palestra demorou demais.
The talk took too long.
Não vi nada de mais no relatório.
I saw nothing unusual in the report.
常见误区
The fixed phrase nada de mais is written separately. With the sense “excessively,” as in falou demais, use one word.
放到语境中练习
从你的真实生活中选一个句子，写两遍：一次用 demais，一次用 de mais。如果两个版本都可以，说明意思怎样变化。