A method of manufacturing foam safety cones utilizes a foam mold to form a plate having several concave holes on the upper surface thereof. The plate thus formed is then taken out of the mold and cut horizontally into an upper plate and a lower plate. The cutting surface goes through the upper edge of the bottoms of the concave holes, so that the upper plate has a mesh shape. The upper plate is further cut into an expanding surface, which is then folded to form a pillar object. Finally, a base is connected to the bottom of the pillar object to render a foam safety cone.