Couch had also finished fifth in the opening round at Beijing, but she scored more than 40 points more in Dubai.
The Plymouth diver eased through the semi-finals with a score of 345.20 points.
Then in a high quality final, she improved on that to finish with 356.60 points.
Couch dived consistently the whole day. Her lowest score in the final was 67.20 points for her third round effort.
China’s Huixia Liu won with a stunning 397.30 points. She was closely followed by her team-mate Yajie Si, who scored 395.15.
Australia’s Melissa Wu, who has returned to her top form, took bronze with 382.60.
Tom Daley will dive in the men’s platform event on Saturday.