The 68-year-old from Bournemouth died when his Vauxhall Astra hit a Nissan Juke on the A31 near Corfe Mullen.
The road, near the Coventry Arms pub, was closed for more than five hours after the crash happened at 13:20 BST.
The driver of the Nissan, a 49-year-old woman from Waterlooville, was seriously injured and airlifted to Southampton General Hospital but police said her condition was not life-threatening.
Three men who were travelling in the Nissan sustained serious but not life-threatening injuries and were taken to Poole Hospital.
Sgt Mark Scammell said: "I would like to thank motorists for their patience during the road closures which are necessary to allow emergency services to deal with the incident."
A man has died in a crash involving two cars on one of Dorset's busiest routes.