Metal materials are widely used in aviation, aerospace, and other fields. At present, a large part of the materials for military and civilian equipment are metal materials. The mechanical properties of metal materials can be tested to understood as the characteristics of materials more comprehensively. One of the common forms of damage to metallic materials is impact damage from low-velocity impacts. Evaluation of the impact properties of materials using a drop hammer impact tester can objectively reflect the reliability of the permissible values of the impact properties of metallic materials, which is of great significance for the design of future aircraft structures. This paper takes the mechanical properties of aluminum–lithium alloy test piece impact test as an example, according to the source of uncertainty in the test results, analyses the reasons for the introduction of uncertainty components and mathematical model, through the calculation of the synthetic uncertainty of each component to finally obtain the extended uncertainty of the impact performance test of the material, which provides a basis for the study of the performance of the aircraft materials and structural design.