Objective: To investigate relative factors for decline of residual renal function(RRF) in patients treated by hemodialysis and discuss protective measures of RRF. Methods: All patients were treated by bicarbonate hemodialysis. Twenty-four hour urine volume, rate of creatinine clearance, increase of body weight between 2 sessions of dialysis and complication of hemodialysis were observed during 6-12months. Results: The decrease of RRF associated with primary glomerular disease was quicker as compared with primary renal tubular intestine disease. The more volume of ultrafiltration is during hemodialysis, the faster decrease of RRF in chronic hemodialysis patients. RRF was more significantly decreased in groups adapted with 1.7m2 dialyzer than that in group with 1.1m2 dialyzer. Conclusion: High ultrafiltration by hemodialysis can induce decline of effective renal blood flow and result in ischemia and reperfusion injury, which may be the primary factor for decrease of RRF at the initial stage of hemodialysis. High effective dialysis had attenuant effect on osmotic diuresis by elimination of solute load and speed up decrease of RRF. Primary glomerular disease, especially on the active phase, also may contribute to decline of RRF.