World No 18 Halep, who has dropped just one set in four final appearances since winning her maiden WTA title in Nurnberg in June, consistently outrallied the former US Open champion with precise groundstrokes.
Stosur, runner-up here last year and champion in Osaka last week, saved 11 break points in the first set before Halep raced through the breaker for the loss of a solitary point.
The 22-year-old fifth seed moved into a 4-1 lead in the second set and sealed the victory in an hour and 41 minutes with a break on her first match point, when the seventh-seeded Stosur netted a return.
"It's an incredible year for me and I am enjoying every moment of it," said Halep, who is projected to break into the top 15 after her latest win.
"Now I already have all of my thoughts about the Tournament of Champions in Sofia.
"It's a very special event for me and I'm preparing thoroughly for it and hope to perform there at my top level."
The beaten Stosur said: "I think it was quite a battle to get to the tie-break in that first set - I was down 3-1 and got it back on serve, which was great. But she really got on top of me in that tie-break, and from then on it was a real uphill battle.
"But all credit to her - she played solid the whole way through today [Sunday]."