Ok. I finally figure out the meaning of dictating， which means "somebody speaks so that others can write down what he or she said". But if I say the Chinese meanings of words while my students write down the English words, is it also " dictation"?
It's translation! (I assume you mean that you say "Beijing" and they write down "northern capital" -- or something like this. This does not amount to dictation.)
To put it another way, dictation involves the students transcribing what you say. If you like, you could call it "a kind of dictation exercise".