The invention belongs to the fields of water conservancy 
engineering, buildings, bridges, sea 
bank revetments, and the like, and particularly relates to a nano modified 
cement-based 
underwater non-dispersible material and a preparation method thereof. The material is prepared from 
cement, mineral 
powder, 
silica fume, a 
superplasticizer, a 
defoamer and other materials, a certain amount of nano-SiO2or CaCO3 and a preferred flocculant are added, the materials are mixed evenly through a mixer, and then 
quartz sand is added to obtain the nano modified 
cement-based non-dispersible material. According to the nano modified cement-based 
underwater non-dispersible material, the fluidity reaches 260 cm, the 
underwater self-leveling can be realized, good dispersion resistance is achieved while high fluidity is achieved, the content of 
suspended matter is lower than 80 mg / L, 1d strength is nearly 20 MPa, and 28 d strength is greater than 50 MPa, and the micro expansion effect is achieved. The nanomodified cement-based underwater non-dispersible material can be in the forms of 
dry powder, wet mixed 
mortar or concrete, and the like, can be made into 
dry powder materials, and can be directly used for underwater construction by being mixed with water added on site, large-scale production and application are achieved easily, and the application requirements of the fields of the water conservancy 
engineering, the buildings, the bridges, the sea 
bank revetments can be met.