you can't
Chat with our AI personalities
No you cannot catch Celebi in Pokemon Emerald.
I got my Celebi for Emerald from the Pokemon 10th Anniversary. You can only get it through Pokemon events, or cheat devices such as Action Replay.
34D56SA7 942DF947
Celebi isn't available in Pokemon Black and White. You have to transfer it into Pokemon Black and White or trade for one.
You cannot catch Celebi unless you are using cheat codes or waiting for Pokemon events.