Objective To explore the influence of different cerebrospinal fluid flow rates on the effectiveness of combined spinal-epidural anesthesia.Methods Two hundred patients undergoing anterior cruciate ligaments (ACL) of knee joint reconstruction with arthroscopy were selected and randomly divided into two groups: group A in which the cerebrospinal fluid flow rate of patients was less than 5 s (n=100) and group B in which the flow rate was above 10 s (n=100). Both groups received combined spinal-epidural anesthesia with 0.5% ropivacain 3 ml, which was diluted with 0.9% normal saline 1 ml.The injection speed was 0.1 ml/s in both groups. Anesthesia was maintained with epidural administration with 2% lidocaine if necessary during operation.Results In group A, the onset of pain block to T8 was earlier than in group B, which was(9.16±0.41) vs (11.97±0.44)min (P<0.05), while the onset time of the highest analgesia plane was(11.12±0.23)vs(15.24±0.22)min (P<0.05).There was no statistically significant difference between the two groups according to the Bromage score for motor block. The effect of tourniquets was excellent in 99% of the cases in group A, which was better than in group B (87%) (P<0.05).Conclusions The cerebrospinal fluid flow rate has much influence on the anesthesia plane and anesthetic effect. A cerebrospinal fluid velocity below 5 s and an injection speed of 0.1ml/s with 0.5% ropivacaine can yield satisfactory anesthetic effect. Anesthesiologists should adjust the drug injection rate according to the cerebrospinal fluid velocity in order to achieve the optimal anesthetic effect.