Abstract: One-sided surcharge loading poses a significant challenge for buried natural gas pipelines, especially in the context of third-party construction, and is frequently encountered within the pipeline engineering field. Buried pipelines subjected to asymmetric surcharge loading and unloading—resulting from surcharge loading on one side and the presence of a trench on the opposite side—are susceptible to considerable stress and potential damage, particularly in soft soil areas. Focusing on X65 pipelines, a three-dimensional finite element model was developed to simulate the effects of one-sided surcharge loading in typical scenarios where a trench is present on one side of the buried pipelines. The analysis examined the influence of the trench on pipeline stress under specific surcharge loading conditions, considering variations in trench depth, width, and length. The results indicate that, in this extreme case, trench depth has the most significant influence on pipeline stress, followed by trench length, while trench width exerts the least influence. These findings provide valuable insights and references for the safety evaluation of buried pipelines subjected to asymmetric surcharge loading and unloading due to third-party construction activities.