© 2022 Elsevier LtdThe behavior of double-glazing unit filled with paraffin wax as phase change materials (PCMs) under fire is studied in this paper. Based on the glass fracture criterion, the mathematical model of PCMs-filled double glazing unit is established, the probability failure conditions of glass fracture under fire load are reasonably set, the thermal structure characteristics of glass structure with paraffin wax layer and hollow glass unit are numerically examined, and the heat transfer characteristics of glass envelope with paraffin wax layer under fire conditions are analyzed. The thermal deformation temperature of glass envelope with paraffin wax layer reaching the fire surface under four fixed boundary conditions and the time of reaching the limit temperature at the edge are respectively delayed by 55 s and 5 s, compared to that of hollow glass unit. The outcomes reveal that the fire resistance of the double-glazing unit filled with paraffin wax is better than that of ordinary double-glazing unit. This research has important implications for the application and popularization of PCMs-filled double glazing unit in building exterior windows.