Objective: To identify distinct trajectories of psychological distress from pre-discharge to 6 months post-discharge in patients with low- and mid-rectal cancer with postoperative LARS and to explore factors associated with different trajectory classes. Methods: A longitudinal study was conducted among patients with low- and mid-rectal cancer with postoperative LARS recruited from a tertiary hospital in Anhui, China, between March 2024 and June 2025. Psychological distress was assessed using the Kessler Psychological Distress Scale (K10) within 3 days before discharge and at 1, 3, and 6 months after discharge. Of the 205 patients who completed the baseline assessment, 178 completed all follow-up assessments and were included in the final analysis. Latent Growth Mixture Modeling (LGMM) was applied to identify distinct trajectories of psychological distress, and multinomial logistic regression was used to examine factors associated with trajectory class membership. Results: Overall, psychological distress declined over time; however, substantial heterogeneity in developmental trajectories was observed. Three trajectory classes were identified: (1) mild-high distress with sustained relief (50.0%), (2) moderate-low distress with fluctuating improvement (28.1%), and (3) severe-persistent high distress (21.9%). Primary caregiver, tumor stage, LARS score, and stigma (SIS score) were significantly associated with trajectory class membership (all p < 0.05). Conclusion: Psychological distress among patients with postoperative LARS demonstrates significant heterogeneity over time. Early identification of patients at high risk of persistent distress, particularly those with severe bowel dysfunction, advanced tumor stage, non-family caregivers, and high levels of stigma, is essential. These findings may inform risk stratification and support the development of individualized nursing interventions targeting symptom management, stigma reduction, family support, and psychological adaptation.