Operational experience of boiler make-up water treatment by using reverse osmosis-mixed bed demin-eralizing system has been described. Practice during the period of four years shows: （1） Settled water pond and three-stage filtration system with mechanical agitation can meet the requitments of reverse- osmosis components to the inlet water quality; （2） It must be considered in the design that the demineralization efficiency of reverse-osmosis components will be decreased about 1%～2% in every year; （3） In normal case

the outlet water from reverse-osmosis equipment shall enter into mixed bed via a decarbonator; （4） The output capacity of the mixed bed must have a sufficient surplus

to avoid its influence on the water supply.