Objectives: Early net ultrafiltration (NUF) rate may be associated with mortality in patients receiving continuous renal replacement therapy (CRRT). In this study, we aimed to tested whether early NUF rates and other factors were association with increased mortality. Methods: We performed a single-center, retrospective, observational study in West China Hospital of Sichuan University (shown in figure 1). We defined the early (initial 24 h) NUF rate as the amount of fluid removal per hour adjusted by the patients’ weight.Using Generalized Additive Model to evaluate the relationship between NUF and mortality (shown in figure 2). Using log-rank test to find cut off point in Kaplan-Meier survival curve in early NUF. We took it as a classified variable (low rate: ≤1.2ml/kg/h and high rate: >1.2 ml/kg/h). The association between 90-day mortality and the NUF rate and other factors was analyzed by cox regression. Results: A total of 684 patients were included in our study. The median NUF rate was 1.04 (interquartile range 0.59–1.75) ml/kg/h and the 90-day mortality was 70.1%. Our results fined that the relationship between early NUF rate (24h) and mortality in critically ill patients receiving CRRT was not “U” (shown in figure 2). Compared with the early low NUF rate, the early high NUF rate (adjusted hazard ratio 1.24, 95% CI 1.04–1.48, p = 0.018) was associated with higher 90-day mortality(shown in figure 3 and table 2). Moreover, we found an increase trend in the 90-day mortality when patients with fluid overload >3000ml(adjusted hazard ratio 1.54, 95% CI 1.19-2, p = 0.001)，Age> 65(adjusted hazard ratio1.84 95% CI 1.51-2.24, p <0.001)，using vasopressor(adjusted hazard ratio 2.24, 95% CI 1.77-2.84, p < 0.001,shown in table 2 ). Conclusions: Compared with NUF rates≤1.2ml/kg/h in the first 24h during CRRT, NUF > rates 1.2ml/kg/h, fluid overload>3000ml,Age> 65 and using vasopressor were associated with higher 90-day mortality.