Natural gas pipeline venting is an indispensable during pipeline repair, reconstruction and extension and risk factors exist in this process. In relocation of the section from AH030+36m to AH030+461m of Ji-Ning pipeline, such operation will be carried out as depressurization, gas venting, nitrogen replacement and natural gas replacement, flare system at Siyang station is determined for ignition and venting. The safety assessment software PHAST6.53 developed by DNV is applied to simulate radiant heat distribution around near the station, valve vaults, structures and buildings within and around the station during the planned venting process and relative formulas are applied to calculate heat radiation intensity. Analyzed and compared are calculation results with simulation ones and analysis results show that in normal circumstances, harm produced during the planned venting process at Siyang station will be within an acceptable range. However, in case of an accident, heat radiation produced from the venting will result in harm on equipment and personnel at Siyang station. It is suggested that more attention shall be paid to equipment and personnel at the station in case of an accident during the venting.