A closed feeder with join alpha-polymerization catalyst suitable for added in is used in chemical, petrochemical and medicine fields, and used for adding poisonous and harmful solid material to a container. A transparent cover is in threaded connection with the upper end of a shell. An annular sealing pad is arranged in the transparent cover and between the transparent cover and the shell. Two holes are symmetrically distributed on the wall of the shell. Left and right sleeves in the shell are respectively fixed in the two holes. A cylinder shaped mouth is arranged at the lower part of the shell. The cylinder shaped mouth is connected with a connecting valve. A gas discharging tube is welded on the wall of the cylinder at the lower end of the shell. A gas empting valve is fixed on the gas discharge tube. The advantages of the closed feeder with join alpha-polymerization catalyst suitable for added in are that poisonous and harmful solid materials can be added into a container or a reactor in confined conditions, the impact on environment can be reduced. The harm to human and environment in the process of feeding is reduced to the minimum degree.