can i wear a sport watch with classic buckle strap

Hi

Any 38mm or 42mm Apple Watch band will fit an Apple Watch of the same size.

Non-Sport bands have various sizes, so check your wrist circumference and refer to the Apple Watch Sizing Guide (which compares all Apple bands) before buying separate bands:

http://www.apple.com/shop/watch/sizing-guide

The Apple Watch Sport also has an anodized aluminum case, whereas non-Sport bands have different metals in their adapters and/or links.

See here for help on how to change bands over: Change your Apple Watch band - Apple Support