Au colloid was prepared by reducing HAuCl4·4H2O with Na3C6H5O7·2H2O. The effects of reductant amounts, mixing procedures, reaction time and stirring speed on the concentration, size, shape and monodispersity of Au colloid were investigated. UV-vis and TEM were used to characterize the size, shape, structure and optical properties of the samples. It's found that the optimal conditions for preparing Au colloid of small size are Na3C6H5O7(aq):HAuCl4(aq)=3:1(V:V), mixing Na3C6H5O7 firstly, reacting for 6 min and 650 r/min stirring speed. The colloid was prepared successfully which has superiority in shape, monodispersity and stability. The size of nanoparticles is only about 6~7 nm