Objective To investigate the status and influencing factors of family function in preschool children with type 1 diabetes mellitus. Methods One hundred and twenty-four preschool children with type 1 diabetes mellitus who were 3-6 years old and were treated at Department of Endocrinology, Genetics, and Metabolism, Children's Hospital, Zhengzhou University from February 2017 to February 2020, including 66 boys and 58 girls, and their main caregivers were selected. According to the family function, they were divided into a good family function group and a poor family function group. The demographic data, clinical indicators, and related scale scores of the family members of the two groups were collected. The children's status quo of family function was analyzed. Univariate and multivariate logistic regression analyses were conducted to analyze the factors affecting family function. t and χ2 tests were applied. Results The overall score of Family Assessment Device (FAD) in the 124 preschool children was (108.24±10.23); 84 children's FAD score ≤ 120; the other 40 children's >120; 67.74% (84/124) had good family function. There were no statistical differences in gender, age, residential address, and family genetic history but were in education level, marital status, family monthly income, medical insurance, fasting blood glucose (FBG), two hours postprandial blood glucose (2hPBG), glycosylated hemoglobin (HbA1c), Family Adaptability and Cohesion Evaluation Scale (FACS Ⅱ-CV), Self-rating Anxiety Scale (SAS), and Self-rating Depression Scale (SDS) between the two groups (χ2=5.560, 9.804, 2.698, and 6.483; t=5.048, 7.469, 3.495, 5.386, 7.482, and 7.220; all P<0.05). Logistic regression model showed that marital status, family monthly income, HbA1c, FACS Ⅱ-CV, SAS, and SDS were independent influencing factors of family function in the preschool children. Conclusions The status quo of family function of preschool children with type 1 diabetes mellitus is relatively weak and needs to be improved. The influencing factors are mainly attributed to marital relationship, family monthly income, blood glucose control, parent-child intimacy and adaptability, and the degrees of anxiety and depression of the family members. Efforts can be made to solve the psychological problems of the children's family members, strengthen blood glucose control and other aspects to improve family function, so that the children can be better cared for.