This paper presents a procedure for preparing a nanofluid which is solid-liquid composite material consisting of solid nanoparticles with sizes typically of 1-100 nm suspended in liquid.By means of the procedure,Cu-H2O nanofluids with and without dispersant were prepared,whose particle size distributions show the stabilization of Cu-H2O suspension with SDBS dispersant is better.Aiming at the dispersion of nano-Cu is regarded as the guide of heat transfer enhancement,surface modification of Cu nanoparticles in water were studied under different pH values and the concentration of sodium dodecylbenzenesulfonate (SDBS) dispersant by the method of zeta potential and particle size.