The Montjuic pool affords stunning views over the Catalan capital and Li held his nerve through a tense battle to produce a superb final dive and extend Chinese domination in the event he won in Shanghai two years ago.
Ukraine's Illya Kvasha took silver, while Alejandro Chavez of Mexico sprang a surprise by pipping Li's team mate Sun Zhiyi to the bronze. It was the first time China had failed to win both gold and silver in four championships.
"When I was younger my coach showed me a video of this pool during the 1992 Olympic Games," Li, who spends a lot of time in Spain and is known back home as 'the Spanish diver', told reporters.
"It was my dream to compete here and of course to dive well," he added.
"I was a bit nervous until the fourth dive but then my coach told me to relax and I made my last two rounds with more confidence."
Li trailed for the first four rounds of the final before moving into the lead in the fifth round with an inward 2.5 somersaults.
He then amassed 87.45 points for his sixth and last dive, a forward 3.5 somersaults, the highest score of the final, to triumph by more than 26 points.
"The other competitors were very strong," Li said. "I was simply luckier today."
Li scored 460.95 points, with Kvasha on 434.30, Chavez 431.55 and Sun 425.05.
Things have not always gone Li's way since his victory in Shanghai and he said suggestions from some quarters that he should retire had proved premature.
"My coach and my team leader always supported me to continue," he said. "They were right! Today, their help paid off.
"Spain is a very special country for me. Since 2005, I came here seven times so this is almost a second home for me."
China have won seven out of 10 one-metre springboard golds since the event was introduced in 1991, with Alexandre Despatie of Canada the last non-Chinese winner in 2005.
(Reporting by Iain Rogers, editing by Clare Fallon)
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