The study investigated the association of multimorbidity patterns with postoperative delirium (POD) in 819 elderly patients undergoing non-cardiac surgery at Nanjing Hospital from January to December 2024. Using latent class analysis, they identified three clinically distinct subgroups of multimorbidity with significant differences in Edmonton Fragility Scale (EFS), Mini-Mental Examination (MMSE) and incidence of POD (p < 0.05). Subgroup 2 increased the risk of POD through frailty with an indirect effect of 0.043 (95% CI = 0.019 ~ 0.070) after adjusting for age and MMSE. A multinomial logistic regression model accurately predicted subgroup membership with AUROCs of 0.993 for subgroup 1, 0.977 for subgroup 2, and 0.990 for subgroup 3; AUPRC were 0.995, 0.886 and 0.974. A specific pattern of multimorbidity in subgroup 2 is associated with frailty, cognitive impairment, and risk of POD. The model offers a tool for preoperative risk stratification.