The time-averaged serum potassium was more comprehensive to reflect the all-time changes of serum potassium levels during peritoneal dialysis (PD). However, the association of fluctuation of time-averaged serum potassium level with long-time survival of PD patients remains unknown. In this retrospective study, we included 357 incident PD patients in 2 centers from January 1, 2007 to October 31, 2012 with follow-up through October 31, 2014. Our data demonstrated that it was the lower time-averaged serum potassium level rather than baseline of serum potassium level that was associated with high risk of death. Patients with higher standard deviation (SD) had significantly poorer all-cause (p = 0.016) and cardiovascular mortality (p = 0.041). Among the patients with time-averaged serum potassium levels below 4.0 mEq/L, a lower mean value was more important than its SD to predict death risk. In contrast, the patients with time-averaged serum potassium levels above 4.0 mEq/L, those with serum potassium SD < 0.54 mEq/L, exhibited a higher 3-year and 5-year survival rate for both all-cause and cardiovascular mortality compared to the control groups. Our data clearly suggested both time-averaged serum potassium and its fluctuation contributed disproportionately to the high death risk in PD patients.