Can you tell me if i could have underbite surgery without braces?

Yes, but: If your upper and lower teeth are both straight, not crowded or spaced, then you might be able to do the surgery without braces. However, usually you would need some form of fixation, where you jaws are wired shut for a period of time.

Probably not: Your teeth have adapted to their current improper bone support. Straightening the jaws doesn't straighten the teeth, does 't allow them to fit, function well after surgery. See an Orthodontist for an opinion as to how surgery alone or surgery + dental position correction would work for you.

Improbable: Orthodontic treatment is almost always needed before and after orthognatic surgery. See an orthodontist first for preliminary consultation and treatment options. The lack of coordination between the orthodontist and the oral surgeon will lead to a compromised result.