Sebastian Steiner and Cartago. © pferdezucht-austria.at
No other details about the fall were available, although the event was suspended after the accident.
Ground Jury president Christina Klingspor said: "On behalf of the whole sport, I would like to extend our deepest sympathy to Sebastian's family."
The horse, Cartago, a 15-year-old gelding, was not injured in the accident. Steiner had ridden Cartago in official events since 2003.
Italian Equestrian Federation president Federico Roman said the accident was "a tragic event".
"Unfortunately horse and rider have obviously incorrectly assessed the obstacle that all five previous combinations had completed without problems."
An investigation is under way into the circumstances of the accident.