In order to study muzzle smoke aggregates of the large caliber barrel weapon, the visible light transmittance of muzzle smoke in open system were measured, and based on it, an equations was derived to calculate characteristic smoke capacity that is proportional to muzzle smoke aggregates.The method was applied to measure muzzle smoke aggregates of a 130 mm cannon.Results show that the minimum transmittance is 0.9%, and the average transmittance 20.1% during launching process, the special smoke quantity is 1830.