The main influencing factors and isotherm adsorption in the treatment of Hg(Ⅱ)-bearing wastewater by using natural magnetite were studied on the basis of the theory of adsorbing heavy metal ions on the surface of water-metal oxides and hydroxides. The results show that the disposal can attain 98% when temperature is 25℃, time is 60min, quantity is 20 g/L, pH is 6.40, grain size is smaller than 200 mesh, ionic strength is zero and Hg(Ⅱ) concentration is 1.12 mg/L and that such factors as pH, ionic strength, quantity, Hg(Ⅱ) concentration, grain size, temperature and time exert different degrees of influence on the disposal, of which the influence of pH is the strongest. The research indicates for the first time that the adsorption isotherm of Hg(Ⅱ) on natural magnetite does not show Langmuir and Freundlich isotherm, but assumes plateau isotherm, which is consistent with the isotherm stepwise ion/coordination particle exchange.