从意义上来说差不多,但是beware的程度比be careful要严重一些.
像接触危险物品,涉及到人身安全之类的一般是用beware.
像过马路,做出慎重决定,情感方面的一般用be careful.
而且be careful的小心多带有“仔细谨慎”的意思.beware更适用于警告.
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贴一些例句给你看：
1. He is extremely careful about his appearance.
他十分讲究外表.
2. He is careful in his speech.
他说话谨慎.
3. After careful consideration, we've decided to accept their offer.
经过慎重的考虑,我们决定接受他们的提议.
4. Be careful crossing the road.
过马路要当心.
5. You should be more careful with your money.
你花钱要慎重一些.
6. Be careful not to/that you don't hurt her feelings.
当心别伤了她的感情.
7. Be careful of the dog; it sometimes bites people.
留心那条狗, 有时候咬人.
8. Be careful (about/of) what you say to him.
对他说话可得小心.
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1. Beware of what you do with this dangerous substance.
你处理这些危险品时,可要当心.
2. Beware wet paint!
注意--油漆未乾!
3. He told us to beware (of pickpockets, the dog, icy roads).
他告诉我们要当心（小偷、狗、结冰的道路）.
4. I was told to beware lest I injure him.
有人关照我,要我小心别伤害他.
5. Beware your hat, lest it should be blown away.
当心你的帽子别被吹走.