Yang, who won her maiden title on home soil in Incheon in 2013, finished two shots ahead of overnight leader Stacy Lewis, two-time champion Tseng Yani and Mirim Lee.
Yang's final round included five birdies with two bogeys for a 69 and an aggregate 15-under 273.
Lewis, who started the day with a one-shot lead, battled Yang throughout the round but fell away on the 15th where she carded a double bogey as her opponent picked up a birdie.
''I was a little bit nervous out there, but I tried to focus on how low I can go today, just focus on my game,'' said Yang.
Former top-ranked player Yani fired a bogey-free 67 to settle for a share of second place.
''I played good, but I missed bunch of putts out there. I was just actually a little nervous out there when I was putting,'' Yani said.
Lewis signed off with an even-par 72, with three birdies against a bogey and a double bogey.
Beatriz Recari had 11 birdies and two bogeys for the year's lowest round at 63, which equaled the course record achieved by five other players, including Lewis and Yani in 2013. Recari finished joint fifth along with Sei Young Kim on 276.