A hollow pot includes a pot unit and a connection unit. The connection unit is a hollow unit and installed to inner surface of a mold set before pressurized air is introduced in the mold set and before the mold set is closed. A probe is inserted into the mold set and blows the plastic material in the mold set. The plastic material expands and contacts against the inner surface of the mold set and seals the connection holes of the connection unit. The plastic material is extended and broken to match upon the connection holes of the connection unit. The plastic material is solidified to form the pot unit. The pot unit is air-tightly connected to the connection unit, and the conjunction area of the connection unit communicates with the space in the pot unit.