Objective To explore the effects of different chemoradiotherapy timing (preoperative or postoperative) on anal functions and stoma outcomes after radical resection for locally advanced rectal cancer (LARC). Methods LARC patients who received chemoradiotherapy combined with radical rectal cancer resection at our hospital between Jan. 2000 and May 2020 were retrospectively enrolled. Patients were assigned to preoperative chemoradiotherapy group (receiving neoadjuvant chemoradiotherapy before surgery) or postoperative chemoradiotherapy group (receiving adjuvant chemoradiotherapy after surgery). The primary endpoint was overall anorectal function at 2 years postoperatively, assessed using the Wexner incontinence score. Secondary endpoints were the proportion of patients undergoing ileostomy reversal surgery. Results A total of 562 patients were enrolled and completed follow-up of at least 2 years, including 247 in the preoperative chemoradiotherapy group and 315 in the postoperative chemoradiotherapy group. The Wexner incontinence scale was fully completed by 422 patients. The 2-year postoperative Wexner score was significantly lower in the postoperative chemoradiotherapy group than in the preoperative group (2.3±4.3 vs 5.3±3.5, P＜0.01), indicating better anal function in the postoperative chemoradiotherapy group. After confounding factors were balanced via propensity score matching, the significant difference in Wexner scores remained between the 2 groups (2.3±4.3 vs 5.3±3.5, P＜0.01). Among all patients followed up, 481 underwent temporary ileostomy, and 369 underwent successful stoma reversal within 2 years after surgery. Multivariate logistic regression analysis revealed that chemoradiotherapy timing was an independent predictor of temporary ileostomy (OR＝0.07, 95%CI 0.03-0.18, P＜0.01) and subsequent stoma reversal (OR＝3.45, 95%CI 2.08-5.56, P＜0.01). Conclusion In LARC patients, postoperative adjuvant chemoradiotherapy, compared to preoperative neoadjuvant chemoradiotherapy, significantly reduces temporary ileostomy rates, improves stoma reversal rates, and is associated with better long-term anal function.