It happened at 8:30 p.m. Saturday at the 55th Deli Market in the 1300 block of North 55th Street.
The video shows the suspect walking into the store, grabbing a drink from a refrigerated shelf, approaching the cash register and pulling out a handgun.
He then grabs the 44-year-old clerk, points the weapon at his head and grins at the surveillance camera.
The suspect then takes money from the cash register and flees.
He is described as a black male in his mid- to late 20s with a thin build, mustache, goatee and side burns.
Police say he has a gap between front teeth and was wearing a black vest with a gray hooded sweatshirt, jeans and a black winter hat. He was armed with a black handgun.
Anyone with information about the crime or the suspect is asked to contact Detective Fegley at the Philadelphia Police Southwest Detective Division: 215-686-3183/3184.