As an important part of the fatigue load spectrum simplification of aircraft structures, small-load omission can significantly save the time and cost of fatigue tests. However, there is no widely accepted standard method for determining the small-load omission level. In this paper, the existing small load omission levels are collected and classified, and determination rules of small load omission levels are analyzed. Then, combined with the general characteristics of aircraft fatigue load spectrum and structural materials, the links between different determination methods of small-load omission levels are investigated, and the correlation model between small-load omission levels is established, providing suggestions and references for the determination of small-load omission levels in the engineering load spectrum simplification.