Objective To evaluate the incidence and severity of atelectasis in elderly patients after laparoscopic surgery by lung ultrasound, and evaluate the guiding role of lung ultrasound in the process of lung recruitment, so as to provide the basis for the application of lung ultrasound in perioperative period. Methods Fortytwo elderly patients undergoing laparoscopic colorectal cancer surgery, aged 6080 years old, falling into ASA physical status Ⅱ or Ⅲ, were selected in our hospital from September 2018 to September 2019. Random control method was used to divide them into control group (C group, n=21) and recruitment group (RM group, n=21). The two groups were scanned by lung ultrasound at 12 regions before anesthesia (T1), at the end of the operation (T2), and 30 minutes after extubation(T3). At the end of the operation (T2), patients with atelectasis in RM group underwent recruitment under ultrasound monitoring, and those in C group did not. Use lung ultrasound scores to assess the severity and incidence of atelectasis. lung ultrasound scores at T1, T2, T3, PaO2, SpO2, operation time, intraoperative blood loss, infusion volume and urine volume were recorded. The same anesthesia method and mechanical ventilation strategy were adopted during the operation. Results The incidence of atelectasis in group C and RM group were 95% and 100% at T2(P＞0.05). The incidence of atelectasis in group C and RM group were 95% and was 50% at T3(P＜0.001). The total lung ultrasound scores of group RM were lower than that of group C (P＜0.001) at T3. The lung ultrasound scores of the RM group were less than the C group in the left 5 and 6 regions, the right 5 and 6 regions at T3(P＜0.05).In RM group, the total lung ultrasound scores at T3were less than it at T2(P＜0.001). 3. PaO2, SpO2. The operation time, blood loss, infusion volume and urine volume were not statistically significant. Conclusion The incidence of atelectasis in elderly patients after laparoscopic colorectal cancer surgery was 100%. Under ultrasound monitoring, lung recruitment can effectively reduce the incidence of postoperative atelectasis, reduce lung ultrasound score, severity of atelectasis and improve lung ventilation.