The invention discloses a pipeline connecting device, which comprises a connecting pipe and a flange II, wherein flanges I are arranged on the two end faces of the connecting pipe; the inner diameter of the flange I is matched with the outer diameter of a connected pipeline; the flange II is connected with the axial end faces of the flanges I; the connecting end faces of the flange II and the flanges I are provided with sealing pieces; the sealing pieces are T-shaped rubber sealing rings; the inner diameter of the flange II is in clearance fit with the outer diameter of the connected pipeline; and the flanges I and the flange II are provided with connecting holes. The pipeline connecting device has the advantages of simple structure, convenience in detaching, wide application range, reliable sealing, saving in time and force and particular suitability for water-containing replacement connection of large-sized pipelines.