A significant number of Chinese and international earthquake disaster surveys indicate active faults as the root cause of earthquakes. Areas along fault lines experience the most severe damage and a greater number of personal injuries compared to regions on either side of the fault. Therefore, by adopting the shallow seismic reflection method to accurately detect the location and distribution of active faults, and developing effective measures to evade active faults, we can reduce earthquake disaster damage and economic losses. On April 20, 2013, the Lushan Ms7.0 earthquake occurred near the Shuangshi-Dachuan Fault (SDF) in the southern section of the Longmenshan fault zone. Because of its relatively high rate of earthquake activity, complex seismo-tectonic environment, and unique geological conditions, achieving usable data with seismic reflection is not easy. For that reason, available shallow seismic data of the SDF is extremely scarce. In our work, we carefully designed a survey to meet the constraints of the project and we have identified the precise location and near-surface structural form of the NE-trending SDF in the disaster area of the earthquake. The seismic surveys were located in Shuangshi Town of Lushan County and Daxi of Baoxing County. The detection of the SDF provided a scientific basis for selecting sites for post-disaster recovery and reconstruction to avoid these active fault zones, and reduce possible disastrous losses that could be caused by future earthquakes.