The theory of the stability of SiO_2 colloid in different electrolyte (NaCl) concen-tration was studied. It was found that the stability of SiO_2 colloidal dispersion was lower with the increase of eletrolyte (NaCl) concentration and the logw-logc relation was straight line. The potential curves in the system were constructed. The stability of SiO_2 colloidal dispersion correspond with the DLVO theory.