The incident happened at around 9am on Sunday in the Finaghy area of south Belfast.
The woman's black Kia Sportage vehicle had become stranded in soft ground when a passer-by helped push the car free.
The man then pulled the woman from the car and made off in the vehicle.
The car was driving down the Finaghy Road in the direction of the Lisburn Road.
It was found abandoned on the Andersonstown Road just after 4pm.
Police said the woman was not physically injured but was left badly shaken by the incident. She had just left a patient's house in the area when it happened.
Detectives are investigating and have appealed for anyone with information to contact them.