think about指"考虑"、"对......有某种看法"，此时它可与think of 换用。但当think of 作为"想起，想到"讲时，of一般不能改为about。如：
Are you thinking about / of moving? 你是不是在考虑搬家？
The old woman often thinks of her son. 那位老人常常想起她的儿子。
think over有"仔细考虑"之意，相当于think about... carefully, 但about是介词,后可直接接宾语。over是副词，所跟宾语是代词时，代词要放在think 和over之间。如：
Let me think it over. 让我考虑一下。