normal map vs smooth?

I create a object and choose smooth for the surface. But when I added a normal map texture on the object, it render the object with flat surface. How do I solve this problem?

We’re going to need way more information than that if you want an answer that isn’t just a wild guess.

What render engine? What are your material and texture settings exactly? What does this normal map look like? How about the object itself, are its object scalings applied? Is the strength of the normal map’s influence appropriate for its size? Screenshots at the very least would help; a .blend file would be better. Remember to pack the image textures into the .blend file before saving if you’re going to share (File>External Data). Post it to www.pasteall.org/blend/ and share the download link here.