This paper is the first investigation on the evaluation methods of flow characteristics in the steady bench. For this purpose, several assumptions used in the steady flow evaluation are examined, comparing the measured and/or processed results by the conventional impulse swirl meter with the ones by the real velocity through a particle image velocimetry. The results show that the most questionable assumption is the solid rotation of swirl. With regard to this assumption, the flow characteristics by the conventional methods are distorted seriously by both of the eccentricity of the swirl center and non-uniform velocity profile along the cylinder radial direction. In addition, the cylinder axial velocity distribution also has the great effect on the flow characteristics.