With the rapid development of China's transportation industry, and now, the treatment of high fill slopes in mountainous regions urgently needs to be addressed. There were many factors that contribute to slope instability, but most slope failures are caused by ineffective treatment of the fill soil, which thereby leads to poor internal drainage and the formation of weak soil layers in the slope, which are prone to large deformation and instability.An analysis was conducted on a high fill slope at an airport in Sichuan before and after reinforcement, monitoring the slope's deformation and displacement. Additionally, FLAC3D finite element simulation software was used to perform a simulation analysis under the most unfavorable conditions. By comparing the analysis results with the actual engineering project, it was found that using a comprehensive treatment method to support the high fill slope significantly improves its stability, providing a reference for similar projects in the future.