1.这两个词一般的区别是：away是表示距离(distance); off
表示分离(seperation)。在表示离开的意味时，away不侧重到什
么地方去；off有由一个地方到另一个地方的含义。
eg: The ship was far away.
    He was away from home.
    We are off in a minute.
2.在go\send\ride\walk\swim等动词之后，away和off都可用，
在意义上没多大区别。
eg: He stayed a long time but went off (away)at last.
    I must sent off (away) a letter.
3.away,off作副词时，因含有动词意味，在俗语中常省去go,
be等词。eg: We must (go) away.
4.在美国的口语中，away用在表示距离，时间的behind,back,
down,up等词前以加强语气。
eg: America was discovered away back in the 15th century.
Notes: away back: as long ago as...
        away down: far down
        away up: far up; a long way up
5.away只能用作副词；off可作副词也可作介词用。
eg: Keep off the grass!
    They took his name off the list.
    Hands off!
    A button is off my coat.
    He is off smoking.