The incident happened in the Petersfield Heath Common car-park, Sussex Road, between 2.15pm and 2.45pm on Wednesday 2 December.
The victim, a 68-year-old man from Clanfield, was waiting to leave the car-park when he was approached by a woman who assaulted him before stealing his Patek Phillipe Nautilus watch.
The suspect then made off into a silver car, which drove east on Sussex Road.
Officers have conducted a number of enquiries and are now turning to the public for help.
Were you in the area at the time? Perhaps you know recognise the woman in this E-fit image?
She is described as being between 20 and 30-years-old, around 5ft 6ins tall and of slim build, with short brown hair. She was wearing a puffer jacket, trousers, a dark blue hat with a brown bobble, and glasses.
Anyone with information is asked to phone 101 with the reference 44200466036.