The robber, who was carrying a gun and a knife, entered the Hillsborough Road business shortly before 10pm on Wednesday.
He threatened employees before making off with cash from the till and cigarettes. It is understood the robber may have driven off in a three-door silver Ford Focus towards Carryduff.
The staff members were badly shaken but unhurt during the robbery.
Police have appealed for anyone who may have seen the car to contact them.