Type 1 cardiorenal syndrome (CRS) is a complication with grave outcomes, and renal replacement therapy (RRT) is an effective rescue therapy. Serum lactate has been correlated with the risk of mortality in patients with sepsis. However, the association between serum lactate level and the prognosis of type 1 CRS patients requiring RRT is unknown. We prospectively enrolled 500 type 1 CRS patients who received RRT from August 2011 to January 2018. The 90-day mortality rate was 52.8% and the incidence rate of RRT independence was 34.8%. Lower pre-dialysis lactate was correlated with a higher rate of dialysis withdrawal and lower rate of mortality. A generalized additive model showed that 4.2 mmol/L was an adequate cut-off value of lactate to predict renal recovery. Taking mortality as a competing risk, Cox proportional hazards analysis indicated that a low lactate level (≦ 4.2 mmol/L) was an independent prognostic factor for the possibility of dialysis withdrawal, as also shown in external validation. The interaction of quick Sequential Organ Failure Assessment score and lactate was associated with dialysis dependence in a disease severity-dependent manner. In summary, we identified that pre-dialysis serum lactate level could predict the possibility of dialysis withdrawal in type 1 CRS patients.