Abstract: A staged cementing device includes a cylindrical body having an inner chamber. A circulating opening and a liquid inlet recess open to the inner chamber are arranged on a wall of the body. An opening assembly is arranged in the body, which has an opening sleeve and an opening seat located in the opening sleeve. Initially the opening sleeve is connected with the body through a first shear pin and covers the circulating opening, and the opening seat is connected with the opening sleeve through a second shear pin and covers the liquid inlet recess. A packer includes a packing valve body and a packer rubber. The packing valve body includes a flow channel in communication with the liquid inlet recess, and the packer rubber includes a liquid reservoir in communication with the flow channel. The second shear pin is sheared off in response to primary cementing procedure.