Based on on-site measurements, the general characteristics of deformation and soil nail stress in the foundation pit of a deep trench warehouse were obtained to address the stability issues of soil nail support beyond current standards. The results indicate that due to the thick layer of fine sand on the upper part of the foundation pit, the horizontal displacement of some measuring points at the top of the slope exceeded the allowable excavation depth limit of 3‰ according to the specifications. The axial force of soil nails increases continuously with the excavation of the foundation pit. Along the length direction of the soil nails, the maximum axial force of the upper soil nails generally occurs in the middle, while the maximum axial force of the lower soil nails often occurs in the middle and deep parts. Some soil nail axial forces even exceed 25% of the sensor range, and the upper filling will further increase the sliding range of the slope. Based on this, an optimization design concept for soil nail support is proposed without increasing the total length of soil nails. By appropriately increasing the horizontal spacing between upper soil nails and decreasing the horizontal spacing between lower soil nails, the support performance of upper soil nails can be fully utilized, the support area of a single soil nail in the lower part can be reduced, and the safety of the entire slope can be improved.