The invention relates to the technical field of installation of seabed immersed tunnels, in particular to an immersed tube section separating device for a seabed immersed tunnel. The immersed tube section separating device for the seabed immersed tunnel comprises an active separating unit and a passive separating unit; a separating jack is arranged at one end of the active separating unit and is used for applying an axial thrust to the passive separating unit, so that the active separating unit and the passive separating unit move relatively, and two immersed tube sections which are connected with each other and are connected with the active separating unit and the passive separating unit are separated from each other; the immersed tube sections cannot be damaged in a separating process; a GINA water-stop belt cannot turn sideward; end steel shells and end sealing doors are not affected; and the distance between the two immersed tube sections are increased as much as possible, and a sufficient safe distance is reserved for follow-up re-floating and twisting movement. The immersed tube section separating device is simple in structure, clear in stress and convenient to design and manufacture.