The purpose of the water quality of pretreatment is to treat the inlet water to reach the water quality index for inlet water that is allowed in the subsequent water treatment facility, in order to ensure the safe and stable operation of the subsequent water treatment facility. Its processing object is suspended solids, colloid, microorganisms, organic matters, residual chlorine and heavy metals etc.. These impurities will produce adverse effect on subsequent equipment (water treatment device of reverse osmosis and ion exchange water treatment device). Such as: Suspended solids will be attached to the exchange resin particle surface, reduce the resin exchanging capacity and produce mechanical blockage to RO membrane; The organic matter will pollute anion resin, make its exchange capacity decline, regenerant consumption increase and the service life of the resin shorten; and will produce Irreversible pollution to RO membrane. The residual chlorine can make the active groups of anode ions exchange resin oxidized and decomposed and destroy the resin structure; It will produce degrade RO membrane and reduce the membrane desalination rate until it is scrapped. Iron ions are easily absorbed by resin and are not replaced by regenerative agent and seriously reduce the resin exchanging capacity; the heavy metal pollution will be produced to RO membrane and will make the membrane accelerate attenuation. Some of the adverse effects above mentioned will decrease water output in industrial water treatment system, shorten the working period, increase the consumption index, improve the cost for water making, shorten the service life of resin and RO membrane, and increase the troubles in operation management. With the continuous development of agriculture and industry, the population of the city has become more and more intensive, a large amount of untreated sewage is discharged into rivers, which has seriously polluted the river source, and has brought great difficulties for tap water treatment work, thus higher requirements is put forward on the pretreatment of the industrial water.