"Good afternoon" is the correct English expression for "中午好的" (which means "Good afternoon" in Chinese).
If you're looking for a more natural or friendly way to say it, you could also say:
- "Good afternoon!"
- "How's it going?" (if you're speaking to someone casually)
- "Nice to meet you!" (if you're introducing yourself)
Let me know if you'd like a different tone or context!