think of 考虑；关心；想起
think about 考虑；研究、思考
think over 仔细考虑 

1、think about 和 think of 这两个短语表示“考虑”、“对……有某种看法”时，可以互换。例如：
 
Don't think of（about）me any more．不要再考虑我。
They're thinking about（of）buying a new car．他们正在考虑买一辆新车。
What do you think of（about）the film？你认为那部影片怎么样？
 
2、 think of表示打算、想出、关心等意义，一般不与think about 互换。
 
Helen，are you thinking of marrying Tom？海伦，你打算和汤姆结婚吗？
Who thought of the idea？谁想出的这个主意？
Lei Feng was always thinking of others．雷锋总是为别人着想。
I can't think of his name．我想不起他的名字。
 
3、think about表示经常思考、研究的意思，一般不和think of换用。
 
I often thought about what you said．我常常想到你说过的话。
I'll think about your suggestion，and give you an answer tomorrow．我要考虑一下你的建议，明天给你答复。
 
4、think over 意为“仔细考虑”。
 
Think over，and you'll find a way．仔细考虑一下，你就会有办法的。
We need several days to think this matter over．我们需要几天的时间把这件事情仔细考虑一下。