American Evelyn Stevens claimed silver with New Zealand's Linda Melanie Villumsen taking bronze.
Just days before her planned retirement from competitive cycling, 36-year-old Arndt retained the title she won last year in Copenhagen in a time of 32 minutes 25 seconds, more than half a minute ahead of Stevens.
Britain's Emma Pooley finished fourth as Arndt shunted her off the podium with the final run of the competition.
Pooley was devastated after failing to upgrade her 2008 Olympic silver medal in London but claimed the suited her perfectly and was an ideal opportunity to regain the title she won in 2010.
Stevens was the early leader and Pooley just failed to overhaul her time to sit second with Arndt and Villumsen still on the road.
Villumsen knocked the British rider down into bronze and Arndt, the time trial silver medallist at London 2012, pushed her out of the medals with a stunning ride.
Other British rider, Wendy Houvenaghel, came 14th.
- Emma Pooley