The 17-year-old scored 181.79 points combined from her short program and free skate at the Figure Skating Korea Challenge at Mokdong Ice Rink in Seoul.
Choi, who won Saturday's short program with 63.04 points, earned 118.75 points in Sunday's free skate.
Kim Ha-nul finished a distant second with 169.15 points, followed by An So-hyun with 162.44 points.
|South Korean figure skater Choi Da-bin performs her free skate at the Figure Skating Korea Challenge, which doubles as the first round of the Olympic trials, at Mokdong Ice Rink in Seoul on July 30, 2017. (Yonhap)|
The Korea Skating Union will hold another qualifying competition in December, and then the national championships in January will be the third and final event for Olympic hopefuls. In the ladies' singles, the top two skaters based on the combined scores from these three events will represent the host country at PyeongChang 2018.
Choi was coming off a strong 2016-2017 season, during which she became the first South Korean to win an Asian Winter Games gold medal in the ladies' singles and earned two Olympic berths for South Korea by finishing 10th in the world championships.
But Choi had a trying offseason. Her mother passed away in June, and problems with a new pair of boots limited her preparations for this competition.
Choi admitted before the event that she'd actually contemplated withdrawing. But once on the ice, Choi skated a clean short program on Saturday and followed that up with another strong performance in free skate Sunday.
Choi opened her free skate with a clean triple lutz-double toe loop combination jump, and nailed her triple flip and double axel. Later in the program, she executed four consecutive jumps, capping off the sequence with a clean triple salchow.
Park So-youn, who was second after the short program, made several landing mistakes in free skate to finish sixth overall with 149.15 points. (Yonhap)