Abstract: Analyzes reasons of sealing packing's leakage in gate valve stem and thinks that it is mainly caused by aging and wearing od valve stem's sealing packing theough its long operational period. Aiming at the problem, compares and selects the properties of such four materials as oil-immersed asbestos packing, flexble graphite, oil-proofrubber and polytetrafluoroethylene. Pracrice has proved that usaling ring made of polytetrafluoroethylene in combination with sealing ring made of oil-immersed rubber can solve the leaking problem of sealing in gate valve stem very well.