Aiming at the demand for separation and purification of tritiated water, a three-column cascade water distillation system has been independently designed and constructed, which is filled with self-developed high-performance packing. During the pilot scale experiment, the treatment of ton level tritiated water was completed at the processing capacity of 5-10 kg/h. The separation effect has been achieved at the detritiation factor higher than 2 000 times and the enrichment factor higher than 20 times. The height equivalent to a theoretical plate of regular packing is 14 cm, and that of random packing is 4 cm. The key parameters vary in a minuscule range during the operation, and the entire system has been running stably for more than 900 h, which can meet the requirements of large-scale engineering application.