Abstract: In aircraft hail impact test, accurate measurement of hail velocity is the key of test success. In this paper, starting from the requirements of aircraft hail impact test and shell velocimetry of secondary air gun, a shading method of hail velocimetry is proposed after analyzing several kinds of shell velocimetry. In analyzing speed measuring device structure, error and structural constraint, details of the design parameters are given. Specific design parameters are D=90 mm, d=2.5 mm, m=8 mm, h=30 mm, r=9 mm~50 mm. Speed error ≤0.75%, less than 1% such test requirements. The result of theoretical analysis and design parameters is applied in velometer development of the first hail test system in China. Velometer fully meets the design requirements is achieved by high speed camera calibration and measurement calibration of the department of calibration test. The theoretical analysis is accurate and reliable.