maybe是副词,只能作句子中的状语.例：或许他是个学生.Maybe he is a student.
而may be则是两个词,may是情态动词,使用时必须后接谓语动词；他大概是个学生.He may be a student.
详解
1.maybe 副词,意为“可能”、“也许”,通常用于句首,有时也放在句中或句末；may be 是情态动词“may”加动词“be”,意为“可能是”、“可能在”等.比较以下各组句子,含义相同,但结构不同：
你也许是对的.
正：Maybe you are right.
正：You may be right.
他可能迷路了.
正：Maybe he has lost the way.
正：He may have lost the way.
正：It may be that he has lost the way.
2.副词 maybe 可单独用作答语,但 may be 不能这样用.如：
A：Do you think he’ll come back?你认为他会回来吗?
B：Maybe.(Maybe not.) 也许会回来吧(也许不会回来吧).