Objective: To analyze the emotional and behavioral problems and associated factors of the only and non only child, and to provide some clues for further monitoring and intervention of psychological and behavioral development among preschool children. Methods: Using a convenience sampling method, a total of 45 065 children enrolled in 153 kindergartens in 23 districts and counties of Chengdu were selected from May to June 2021 to investigate demographic characteristics and children s psycho behavioral development through online questionnaires filled out by their guardians. The Chi square tests were used to analyze whether the differences in abnormality rates of each dimension were statistically significant between the only and non only children. The emotional and behavioral problems of only children and non only children were analyzed by propensity score measurement. Results: The detection rate of abnormal emotional behavior problems in children was 6.10%, including 6.34% in the only child group and 5.84 % in the non only child group. After matching, total difficulty score, and scores of emotional symptoms, conduct problems, hyperactive attention deficit, peer interaction, and social behavior differed between the only child group and the non only child group ( t =9.91, 8.97, 3.91, 15.57, -5.46, 4.08, P <0.01). Conclusion In terms of the total score of difficulties, emotional symptoms, moral problems, and hyperactivity attention defects, the non only child is better than the only child，but the opposite is true in terms of peer interaction and social behavior. Mental health conditions among the only child should be paid more attention. Whether or not the only child should be taken as an important consideration for preschool children s mental health care.