'How do you do?' 'How are you doing?' What's the difference？ Note the corrections I've made to your question. The answer to your question is this - they are very different indeed. 1. 'How do you do?' This is a rather outdated and formal expression meaning 'It's a pleasure to meet you'. A conversation might go like this: A: Bill, this is my colleague, Charles. B (to C): How do you do? C ( to B): How do you do? This would probably be accompanied by a handshake between B and C. As you can see, 'How do you do?' is not a genuine question, because the response is to repeat 'How do you do?'. You would only use this on the first occasion you meet someone, and only in a formal context. 2. 'How are you doing?' is a question, and it's an informal variant on 'How are you?'. For example: A: Hi. How are you doing? B: Great. How are you doing? A: Not bad.

How do you do is more formal. How are you doing is more casual. Also you migh say how are you doing Zhou. Where as you might say how do you do, my name is Zhou. When addressing someone you don't know. But when it comes down to it in America both are ok.

thank you I think I know

"how do you do" is still used in business meetings certainly in the Uk, as is the equally common "grunt" "How are you doing" comes from "Friends" and is what Joey uses as his "Pick up line" probably not best in a business environment. Or possibly only when meant ironically