Ruolin opened with a 10 as she made five fantastic dives to score 422.30 points and beat 16-year-old Australian Brittany Broben by 55.8 points.
Pandelela Rinong picked up bronze with 366.50 to secure Malaysia's first ever Olympic diving medal.
Chen, who won the platform synchro with Wang Hao, now has four golds in total.
She won the individual and synchronised events as a 15-year-old at Beijing four years ago and was unchallenged in the preliminaries, semi-final and final in London.
British record holder Monique Gladding and compatriot Stacie Powell failed to qualify for the semi-finals. They finished 19th and 20th, with only the top 18 progressing.
China's Chen Ruolin defended her women's Olympic 10m platform diving title in dominating style to claim her second gold medal of London 2012.