Studying on change of serum beta2microglobulin, some others and complications of 32 chronic renal failure patients treating with maintenance hemodialysis using hemodiafiltration online with once per 2 weeks compared with those of hemodialysis patients using high-flux dialyzer, the result shows that after dialysis secsion serum beta2microglobulin of hemodiafiltration online is significantly decreased compared with time before dialysis secsion (69.2 percent 17.3 mg/I versus 21.8 percent 6.9 mg/I), p 0.001. Reduce level of beta2-microglobulin of hemodiafiltration is much than that of hemodialysis using high-flux dialyzer, p 0.01. After 6 months, reduce level of beta2-microglobulin of hemodiafiltration is also much than that of hemodialysis using high-flux dialyzer (from 69.2 percent 17.3 mg/I down to 32.4 percent 9.1 mg/I compared with from 64.8 percent 19.4 mg/I down to 46.7 percent 12.8 mg/I), p 0.01. Hemodiafiltration online makes good treating anemia, increasing of BMI, reducing complications such as hypotension, dialyzer block and muscle cramps compared those of hemodialysis, p 0,05.