The invention discloses a preparation method of a high-strength cement-based board having low water cement ratio. Even cement and water mixing is achieved under the condition of low water cement ratio, no unnecessary free water exists, the water demand is small, the prepared high-strength cement-based board having the low water cement ratio only have a small number of fine holes internally, is high in compactness, low in pore rate (2.0%-8.0%), small in aperture size (5 nm to 50 microns), high in strength and better in waterproofness, corrosion resistance and anti-freezing property.