The invention relates to a pH (pondus hydrogenii) adjustable ion exchange device and a pH adjustment method. The ion exchange device structurally comprises a carbon steel lined tank body, wherein thetank body is fill with an ion exchange resin bed comprising weak anion exchange resin. The pH adjustment method comprises the steps of mixing and allowing system influent and regenerated resin in a water inlet pipe of a system to enter into the tank body from a water inlet, after adequate exchange by the ion exchange resin bed, allowing a system effluent collector to collect the system influent and the regenerated resin, discharging the system influent and the regenerated resin from a water outlet to form system effluent, and discharging the failing resin from a resin discharge pipe. The device and the method have the advantages that: 1) a controllable ion exchange degree can be achieved; a brand-new application way is created for an application scope of ion exchange, and 2) when the device and the method are applied to a reclamation system of wastewater containing acid and alkali, salt in the water is reduced in a pH adjustment process of the treated water, more superior conditions can be provided for subsequent recovery treatment, and the device and the method contribute to lowering operating cost of the whole system and increasing a recovery rate of the system.