Objective To investigate the effect of lactulose in bowel preparation for constipated patients.Methods A comparison was made between 200 constipated patients at the main branch of Suzhou Municipal Hospital from June 2021 to August 2023.Patients were randomly divided into a treatment group and a control group.The treatment group used lactulose in combination with polyethylene glycol electrolyte powder(PEGP) for bowel preparation,while the control group used only PEGP.The bowel preparation effectiveness,tolerance,and adverse reactions of the two groups were compared,and blood potassium levels were analyzed.Results The bowel preparation effectiveness rate in the treatment group was 90%,which was significantly higher than the 64% in the control group(P<0.05). The tolerance rate in the treatment group was 78%,higher than the 43% in the control group(P<0.05). The adverse reaction rates in the treatment and control groups were 24% and 21%,respectively,with no significant difference(P>0.05). There was no significant change in blood potassium levels before and after the examination in both groups(P>0.05).Conclusion Lactulose can improve the bowel preparation effect for constipated patients,enhance tolerance,and does not affect blood potassium levels.