The aim of this study was to develop a model of generalized anxiety disorder in preschool children in Tehran. The present study was conducted in a qualitative method using a grounded theory approach. 19 child specialists (psychologist / psychiatrist) were selected by purposeful sampling method.  Data were collected through semi-structured and interactive interviews to reach information saturation. MAXQDA version 18.2.0 software was used for data analysis. In open coding, 141 primary codes were obtained, which were categorized into 21 thematic categories based on thematic similarity, in axial coding. In the third stage or selective coding, generalized anxiety disorder was identified as the central or major variable. Understanding the causes of generalized anxiety disorder can help families, therapists, and mental health policy-makers to improve the conditions that cause the disorder.