In order to ensure the safety production of offshore heavy oil thermal recovery platform and establish the mathematical model of thermal recovery blowoff diffusion of offshore platform, ANSYS Fluent software was used to simulate the gas diffusion in the process of steam huff and puff thermal recovery, quantify the impact of thermal recovery blowoff process on the platform, and provide guidance for platform general layout. Taking LvDa 21⁃2 oil field as an example, due to the increase of methane content in the later stage of blowout, the slow diffusion rate caused by the decrease of blowoff volume, blowoff was easy to accumulate in the steam boiler and other higher equipment, thus causing potential safety hazards. By optimizing parameters of cold vent system and equipment layout, the impact of blowout on safe operation was lowered to the utmost and platform area was cut down by 5.9%. The study could provide reference for safety design of offshore thermal discovery platform.