A method for classifying the shapes of sound radiator is presented. It assumes that sound field can be measured by a linear array. A sound field, due to the radiator vibrating with uniform velocity, can be determined by its shape, size, and orientations. Measured data also can be varying from the array's position. To predict the shape of radiators from these measured data, mathematical relation between geometric parameter and measured information is needed.Assume that a radiator is cylinder,the magnitudeand phaseof measured pressure is related with the lengthand diameterof radiator,respectively.In this paper, the method for estimatinglength and shape of a finite cylinder by using its radiated pressure is proposed and verifiedthrough experiment.