The invention discloses an in-barrel bag for packaging liquid food. The in-barrel bag comprises a bag body, a bag neck and a bag opening, wherein two ends of the bag neck are respectively in heat seal connection with the bag body and the bag opening suspended on a barrel opening. The in-barrel bag can be sealed by using an inducing aluminum film after being filled. The in-barrel bag for packaging liquid food, provided by the invention, is folded into a flat strip, and can be orderly unfolded in a filling process, thus the volume of an outer barrel is fully utilized, a plastic bag opening is firm and can ensure that liquid is poured smoothly, and an empty bag is taken out conveniently. Finally, the liquid food in the bag cannot be in contact with the outer barrel, and thus the food packaging requirement is met.