The teenager becomes the club's fourth foreign player for the 2012-13 season, and will add pace and movement to the champions' left side of midfield
An Under-20 international, the 19-year-old left-sided attacker becomes the fourth visa player in the club's squad, and the third new signing - along with Ben Halloran and promoted goalkeeper Matt Acton - for the Roar ahead of the coming campaign.
Dong trialled at the Roar in May, having also spent time at the Newcastle Jets in March and April.
He fills coach Rado Vidosic's need for a left-sided midfielder to complement Halloran on the right flank, and joins from Kyung Hee University in his homeland.
"He's a very exciting young player," Vidosic said in a statement. "We felt that we needed another left-footed player with a more direct style of play to compliment what we already have got.
"Now, we've got more combinations we can apply and I'm very excited about that."