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The 30-year-old and her horse Valegro scored a superb 87.577% - just short of their world-record score of 88.022%.
The special test is an event in its own right but also a qualifier for Sunday's showpiece freestyle test, set to music.
The pair had helped Great Britain to team silver on Friday behind the Netherlands.
"Today, he felt on great form and I knew I just had to go in and ride him. I had a good ride from start to finish," said Dujardin.
"It's tough with a German crowd. They really get behind their riders - a bit like we had in London - and coming here and doing it is amazing.
"I have to remember that this is my passion and what I love, and that's how I keep the nerves from kicking in. I know I have to go in there, nail it and do my best, but today I really did enjoy it."
Dujardin's team-mate Carl Hester finished fifth after scoring 77.003% on board Nip Tuck while Fiona Bigwood and her horse Atterupgaards Orthilia were ninth on 74.210% to also qualify for Sunday's finale.
Michael Eilberg, who was 19th on Marakov (69.930%), misses out with only the top 15 to go through.
Dujardin, who also holds World and Olympic titles, had an anxious wait with Dutch world number two Edward Gal the last rider to go. He was forced to retire after a problem with his horse.
Germany's Kristina Broring-Sprehe took silver on Desperados FRH (83.067%) with Dutch rider Hans Peter Minderhoud third on Glock's Johnson TN (79.034%).
Britain's Charlotte Dujardin has successfully defended her Grand Prix Special dressage title at the European Championships in Aachen, Germany.