The aim of this study is to examine, identify, and analyze the key factors influencing customer behavior patterns in the banking system. This research was conducted using a qualitative approach and thematic analysis. Data collection and extraction of relevant themes were carried out through semi-structured interviews with key experts in this field. Participants were selected using purposive sampling and the criterion of theoretical saturation, based on which 12 individuals were chosen, including university professors in the fields of marketing management and business, as well as heads, deputies, and customer relationship managers from Day Bank branches in Tehran. To ensure the validity and reliability of the data, two methods were employed: participant review and expert review by non-participating experts in the research. For data analysis, MAXQDA statistical software was used, and the data were examined through thematic analysis. The results of this study indicate that customer behavior patterns in the banking system are structured into four main categories (banking services, financial affairs, branch characteristics, and human and relational factors), 10 subcategories (electronic banking, quality and variety of banking services, foreign exchange and international activities, banking facilities and interest rates, investments, interior and exterior branch design, branch accessibility and amenities, customers, human resources, marketing and advertising), and 66 indicators.