Abstract: Heater for crude oil is a main energy consumption facility in long-distance oil pipeline. However, low efficiency can be seen. The factors affecting the heat efficiency are screened by numerical calculation and verification calculation. Results show that heat loss due to the incomplete combustion is monotone decreasing along with the excess air ratio. The heat loss is lower than 0.5% when the ratio is higher than 1.2. The heat loss in incomplete combustion also occurs when volumetric thermal load is higher or lower, and the optimal value of it is 70~110 kW/m³. The verification calculation shows that no matter how high or low the excess air coefficient and thermal load ratio are, they will result in low heat efficiency. When they are at 1~1.2 and 0.6~1.1, respectively, the heat efficiency will be high. After oil-fired heater is changed into natural gas, the heat loss in flue gas will increase to decrease the heat efficiency of heater.