The 22-year-old, skating in only her second competitive event in almost two years, stormed to victory with a total of 210.77 points after a dazzling free programme in Seoul.
"I settled down once the music started and I tried to skate like I had in practice," Kim told local reporters after battling nerves following a rare fall in Saturday's short portion.
"I didn't think I could get over 200 points but I was able to stay composed. The world championships are coming up and I'm hoping to stay healthy and prepare the best I can."
The world championships take place in London, Ontario from March 10-17. Kim won the world title in 2009 and took silver in 2010 and 2011.
South Korea's ice queen, who stormed to Olympic gold three years ago with a world record 228.56 points total, announced her comeback to the sport after more than a year away last summer.
Kim, who plans to hang up her skates after the 2014 Sochi Olympics, scored 201.61 points to win an event in Germany last month in her return to competition.
She blamed her silver behind Japan's Miki Ando at the 2011 world championships on the weight of expectation in Korea, where she is arguably the biggest name in sport.
Fifteen-year-old Park So-youn finished runner-up behind Kim on Sunday with 161.88 points with Choi Da-bin, just 12, third on a total of 153.09 points. (Reporting by Alastair Himmer in Tokyo; Editing by John O'Brien)
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