Net ultrafiltration (UFNET) during continuous renal replacement therapy (CRRT) is often used to treat fluid overload (FO) in critically ill patients, but the effect of UFNET intensity on the prognosis of critically ill patients remains unclear. This article reviews the effects of FO on critically ill patients and the effects of different levels of UFNET on organ function, mortality, dialysis dependence, and potential tools that may be used to guide the adjustment of UFNET to draw clinicians' attention to the optimal UFNET intensity during CRRT treatment.