If Miles' Last name is straume then why his father's Last name is Chang?

There are about four possibilities: 1) Miles took his mother's maiden name. 2) Miles' mother changed their last name to avoid trouble from the Others or Widmore or the Shadow of the Statue people. 3) Miles' mother remarried and Miles took the last name of his stepfather. 4) Miles changed his last name to Straume possibly because it sounds like maelstrom. I can imagine Rufio-looking young rocker Miles changing his name because it sounds bad ass.

Miles may have taken is mothers maiden name.

I agree its probably his mums maiden name. Its the same with Ethan he always said his last name was rom and his fathers name is goodspeed.

he probably got re-married.His dad anyway, or he couldve. I havent watched it in a while. So i need to start catching up...