To optimize the combustion system of oxygen-fuel glass fiber furnace and improve the heat transfer efficiency of the furnace, this paper uses numerical simulation methods to investigate the effects of two combustion methods, the top firing furnace and the side firing furnace, on the temperature field within the combustion space, flue gas flow field, glass temperature field, and heat transfer efficiency of oxygen-fuel glass fiber furnace. The results indicate that， the flame of the top firing furnace is concentrated, resulting in pronounced temperature variations within the combustion space. In contrast, the side firing furnace features flames uniformly distributed along the length of the furnace. As a consequence, the overall temperature of the combustion space in the side firing furnace is higher than that in the top firing furnace. The side firing method is more likely to result in a higher degree of high-temperature corrosion on the refractory materials of the crown and breast wall. The prolonged presence of high-temperature flue gas in the combustion space of the side firing furnace is advantageous for facilitating heat exchange between the flue gas and the airflow, as well as refractory materials within the combustion space. The statistical analysis reveals that the side firing furnace exhibits a lower average flue gas temperature at its exits. The side firing furnace demonstrates a more uniform temperature distribution of molten glass along the width of the furnace. The average temperature of the molten glass in the top firing furnace is 1 531 ℃, exceeding the average temperature of 1 523 ℃ observed in the side firing furnace. The top firing furnace exhibits a heat transfer efficiency of 52.3%, surpassing the heat transfer efficiency of 51.9% observed in the side firing furnace. This implies that, under identical conditions of natural gas supply, electrical melting assistance, and molten glass melting capacity, the higher heat transfer efficiency in the top firing furnace is attributed to the direct interaction of the burner flame with the molten glass and batch layer.