Emergency services crews responded to an incident at around 1pm when a lorry entered the River Avon off Ringwood Road, North Gorley.
Hampshire Police, South Central Ambulance Service and Hampshire & Isle of Wight Fire and Rescue Service were called to the scene while the road was closed for a number of hours.
The driver, a man in his 60, was pronounced dead at the scene
The force said enquiries are ongoing to establish the circumstances surrounding his death.
The driver’s death comes following severe flooding across Dorset.