In order to study the relation between fragment drag coefficient and flight velocity, the standard steel balls were chosen as spherical fragments and the simulated shell was designed as launching device to study the air drag coefficient of spherical fragment, the velocity attenuation regularity of spherical fragment was studied, and the variation rule of spherical fragment's drag with flight velocity was deduced. The research results show that by the design of test facilities and test system, and combining theory analysis with test measurement, the variation rule of spherical fragment's flight velocity can be studied precisely.