The invention provides a method of sealing a carbon dioxide seabed salt water layer by using hydrate sealing, which belongs to the technical field of greenhouse gas emission reduction. Carbon dioxide is injected to the seabed salt water layer via an injection device, the injected carbon dioxide moves to the upper layer of the salt water layer under effects of a buoyancy force, a carbon dioxide gathering zone is formed under sealing effects of a covering layer, a small part of carbon dioxide escapes to a sea sediment via a geological fracture of the covering layer and is combined with water in the sediment under effects of formation pressure and temperature, carbon dioxide hydrates are formed, a hydrate layer is formed in the sediment, the carbon dioxide can be prevented from further escaping, and a tiny part of carbon dioxide escaping to deep sea water is dissolved, and complete sealing is realized. According to the method of the invention, a sea sediment with a proper water depth is selected to control the carbon dioxide hydrate generation condition, the carbon dioxide leaking to the sediment can form hydrate sealing, and thus safe sealing of the carbon dioxide can be realized.