Heavy metal wastewater mainly comes from the wastewater discharged by mining, smelting, electrolysis, electroplating, pesticide, medicine, paint, pigment and other enterprises. The types, contents and existing forms of heavy metals in wastewater vary with different production enterprises. Because heavy metals can't decompose and destroy, they can only transfer their existing position and change their physical and chemical forms. For example, after the chemical precipitation treatment, the heavy metals in the waste water are transformed from the dissolved ion form to the insoluble platform and precipitated, and transferred from the water to the sludge; after the ion exchange treatment, the heavy metals in the waste water are transferred to the ion exchange resin, and then transferred from the ion exchange resin to the regenerated waste water. Therefore, the principle of heavy metal wastewater treatment is: first, the most fundamental is to reform the production process. No or less toxic heavy metals are used; second, reasonable process flow, scientific management and operation are adopted to reduce the amount of heavy metals and the loss with the waste water flow, and the amount of discharged waste water is minimized. Heavy metal wastewater should be treated on site at the place where it is produced and mixed with other wastewater to avoid complicating the treatment. Moreover, it should not be directly discharged into urban sewers without treatment to avoid expanding heavy metal pollution. The treatment of heavy metal wastewater can be generally divided into two categories: one is to transform the dissolved heavy metal in the wastewater into insoluble metal compounds or elements, which can be removed from the wastewater by sedimentation and floatation. The methods can be applied, such as neutralization sedimentation, sulfide sedimentation, floatation separation, electrolytic sedimentation (or floatation), membrane electrolysis, etc.; the other is to remove the heavy metal in the wastewater Under the condition of changing its chemical form, it can be concentrated and separated by reverse osmosis, electrodialysis, evaporation and ion exchange. These methods should be used separately or in combination according to the quality and quantity of wastewater.