Objective To explore the threshold effect of life space level on social alienation among elderly patients undergoing maintenance hemodialysis (MHD), and to provide evidence for developing precise and actionable intervention strategies. Methods A convenience sample of 318 elderly MHD patients were recruited from three general hospitals in Kunshan.Data were collected using a general information questionnaire, the Chinese version of the Life Space Assessment, and the General Alienation Scale.Hierarchical linear regression was performed to examine the influence of life space level on social alienation, then smoothing curve fitting and threshold effect analysis were used for the identification of cut-off point. Results The sample scored （57.00±19.69） for life space, and （40.26±7.31） for social alienation.Hierarchical linear regression showed that, after controlling for general demographic va-riables, life space was a significant influencing factor for social alienation (P＜0.05).Smooth curve fitting revealed a nonlinear association between life space level and social alienation (P＜0.05), and when the life space score greater than 78, social alienation decreased progressively with increasing life space scores (P＜0.05). Conclusion Elderly MHD patients exhibit a moderately high level of social alienation and a low level of life space.A life space score of 78 may serve as a critical cutoff point for targeted social alienation interventions.