In view of problems that limit values of projectile's structural characteristic parameters and eccentricity can't be calculated, projectile motion in external trajectory, especially the limited ballistic environment which is important for fuze design can't be analyzed accurately, the method of fitting and resea ching mathematical distribution of projectile's mechanics parameters according to the measured data was proposed here. A 82 mm-caliber mortar projectile's five kinds of mechanics parameters do not obey normal distribution. Axial centroid position and polar moment of inertia do not obey Weibull distribution either. But eccentricity, mass and moment of inertia of the equator obey three-parameter Weibull distribution, and eccentricity further obeys Rayleigh distribution.