A rolling model is established to describe the velocity attenuation law of triangular prism-shaped prefabricated fragments with large aspect ratio from supersonic to subsonic in the rolling state. The equivalent upwind area method is contrasted under numerical calculation and launch test. The results show that the experimental results are consistent with proposed method but have large deviation from the equivalent upwind area method. It is proved that the rolling of the large aspect ratio fragments can’t be ignored during the movement, and the equivalent area method will cause large deviation or distortion of the calculation result.