The invention belongs to the technical field of building materials, and specifically relates to an underwater concrete. The underwater concrete is prepared from cement, sulphate aluminium cement, a concrete modifier, slag, silica fume, fly ash, aggregate and mixing water according to a certain ratio. The underwater concrete, which is prepared from a modified cement-based gelling composite material, is not easily dispersed under water; moreover, the fluidity of the underwater concrete is good, the coagulation is quick, the structure of the concrete is compact, the one-day compressive strength is 5 to 40 MPa, and the 28-day compressive strength is 20 to 90 MPa. The high performance underwater concrete is suitable for the mechanical operation mode comprising steps of strong stirring and large-powder pumping, the work efficiency can be improved, a novel building material is provided for the building of large area underwater concrete in a short time, the underwater concrete is especially suitable for the construction and repairing of underwater projects, and at the same time the provided underwater concrete is also suitable for the engineering projects in islands, which are lack of construction sands and fresh water, have a long transportation distance, and are far from the mainland coastline. The preparation method is simple, and can be widely used.