Objective To investigate the effect of ultrasound guided quadratus lumbaris block (QLB) on pain and sleep quality in patients undergoing laparoscopic colorectal surgery.Methods 80 patients who underwent laparoscopic colorectal surgery at Huai'an Second People's Hospital from January 2019 to January 2022 were selected and randomly divided into an observation group and a control group, with 40 patients in each group. Under ultrasound guidance, the control group underwent abdominal transverse fascial block (TAPB), while the observation group underwent bilateral QLB. Compare perioperative indicators, heart rate (HR) and blood pressure [systolic blood pressure (SBP), diastolic blood pressure (DBP)], sleep quality [was assessed using the subjective sleep quality score] pain level [evaluated using visual analogue scale (VAS)], immune function [CD3+, CD4+, CD8+, CD4+/CD8+], and adverse reactions, as well as the use of postoperative painkillers.Results The dosage of remifentanil, the first postoperative exhaust and defecation time in the observation group were lower than those in the control group, and the difference was statistically significant (P<0.05). There was a statistically significant difference in the levels of SBP, DBP, and HR between the two groups of patients at the inter group, time point, and inter group time point interactions (P<0.05). The subjective sleep quality score of the observation group patients was significantly higher than that of the control group (6.13 ± 1.54), with a statistically significant difference (t=13.904, P=0.000). The VAS scores of the observation group patients at rest and activity at 1 hour, 6 hours, 12 hours, and 24 hours after surgery were lower than those of the control group, and the difference was statistically significant (P<0.05); There was no statistically significant difference in VAS scores between the two groups of patients at rest and during activity 48 hours after surgery (P>0.05). The levels of CD3+, CD4+, CD8+, CD4+/CD8+in the observation group were higher than those in the control group 24 hours after surgery, with statistically significant differences (P<0.05). The incidence of adverse reactions in the observation group was significantly lower than 42.50% in the control group, with a statistically significant difference (P<0.05).There were 8 patients (20. 00%) in the observation group who applied painkillers after surgery, while 18 patients (45. 00%) in the control group. There was a significant difference between the two groups（χ2=5.698, P=0.017).Conclusion Ultrasound guided QLB can effectively alleviate postoperative pain and improve postoperative sleep quality in patients undergoing laparoscopic colorectal surgery, with high safety.