A method for concentrating and treating low-discharge waste water comprises that two-stage continuous electric desalinization device to concentrate and treat the low-discharge waste water, water enters into a purifying stage continuous electric desalinization device, adding voltage, the outlet fresh water of the purifying stage can avoid radioactive ion, and the outlet dense water of the purifying stage is circulated to the dense water inlet of the purifying stage to be discharged partly, and the water is fed and discharged in same amount, the fresh water inlet of the concentrate stage is the dense water outlet of the purifying stage, the fresh outlet water of the concentrate stage is feedback to the fresh water outlet of the purifying water to be treated, the dense water outlet of the concentrate stage is partly circulated to the dense water inlet of the concentrate stage, to be discharged partly, and the dense outlet water passing the purifying stage is fed with same amount as the discharged water, the discharged dense water of the concentrate stage is the concentrate waste water of the whole system. The invention has the advantages in high concentrated ratio of radioactive waste water, low generated amount of secondary radioactive waste, low cost and automatic control.