Abstract: In order to study the influence law of natural gas transportation parameters on temperature field in the heat affected zone of in-service welding in X80 natural gas pipeline, the X80 natural gas pipeline with a diameter of 1 422 mm and a wall thickness of 25.7 mm was studied and the temperature field during its in-service welding was numerically simulated with the finite element method. The results show that the process of temperature drop from 800 ℃ to 500 ℃ in the heat affected area (with the time required expressed as t_8/5) appears within the depth of 10 mm in the first 20 s of in-service welding. Besides, the natural gas transportation temperature has the greatest impact on the temperature field of pipeline. When the transportation temperature is less than 10 ℃, t_8/5 decreases sharply as the temperature drops, and it is as low as 2.5 s when the transportation temperature is -50 ℃. Further, the transportation pressure and flow rate of natural gas have little effect on t_8/5, and t_8/5 decreases slowly with the increasing of transportation pressure and flow rate of natural gas. When the transportation temperature is less than 10 ℃, the flow rate is greater than 10 m/s, and the pressure is higher than 10 MPa, the heat affected zone and the welds are at a high risk of cold cracks. The research results could provide a theoretical basis for the on-site construction organizations to control the parameters such as the transportation conditions and welding technology for in-service welding of X80 pipeline, which is helpful to ensure the safe operation of in-service welding of X80 pipeline.