Objective To evaluate the efficacy and safety of polyethylene glycol electrolyte powder （PEG） combined with linaclotide （Lin） for bowel preparation in elderly constipated patients before colonoscopy. Methods In this prospective， randomized controlled trial， 90 elderly patients with constipation undergoing colonoscopy were recruited at our hospital from June 2022 to December 2023. Participants were randomly assigned to three groups （n = 30 each）： PEG-3L alone， PEG-3L + Lin， and PEG-2L + Lin. Primary outcome was Boston Bowel Preparation Scale （BBPS） score and secondary outcomes included adverse event rates， colonoscopy completion rate， withdrawal time， and polyp detection rate. Statistical analysis was performed using independent t-tests and chi-square tests. Results The PEG-3L + Lin group achieved significantly higher BBPS scores than both PEG-3L alone and PEG-2L + Lin groups did （both P < 0.001）. The PEG-2L + Lin group also outperformed the PEG-3L alone group in cleansing efficacy （90.0% vs. 76.7%， P = 0.008）. The PEG-2L + Lin group demonstrated the best tolerability and lowest adverse event rate， the PEG-3L group had the longest withdrawal time （P < 0.05）， but the three groups showed no significant difference in polyp detection rates. Conclusion PEG combined with linaclotide significantly improves bowel cleansing in elderly constipated patients. PEG-2L + Lin regimen provides optimal balance between efficacy， safety， and tolerability， making it a preferable choice for this population.