The invention relates to a device for preventing backwater and odor for an indoor outfall, belonging to the building drainage field. The invention comprises a sewer outlet (1), a sewer outlet edge (3), a bevel sleeve gasket (4) which is covered on the lower part of the sewer outlet edge, three double-bevel grooves (4), high elastic flat hermetic sewer soft sleeves (5) with the upper parts covered on the positions of the three double-bevel grooves, sleeve skins (6) which are adhered on the lower parts outside a plane of the high elastic flat hermetic sewer soft sleeves, and collapsing sleeves (7) which are fixed between the sleeve skins and the soft sleeves. The device for preventing backwater and odor for the indoor outfall has the advantages of simple structure, low manufacturing cost, fast drainage, water conservation, backwater and odor prevention and good sealing effect, enables a lavatory pan, a urinal, a basin, a vegetable sink, a mop sink and so on to save a drain trap, thereby saving materials and facilitating the dredging of the sewer.