The determination of point spread function ( PSF ) is essential for the assessment of the performance of multi-slice CT corresponding to particular scanning or reconstruction condition. We studied the accuracy of the method for determination of PSF. The precision were evaluated with use of special made phantom and computer simulations. The PSF of some kinds of multi-slice CT were evaluated under the several scanning or reconstruction conditions. The performances were compared with each other and discussed. The PSF ( x, y, z ) was measured with separate components of PSF ( x, y ) and LSF (z). In the measurement of PSF ( x, y ) and LSF (z), we used Boone phantom and delta phantom respectively. The PSF ( x, y ) was calculated from LSF (x) and LSF (y). The LSF ( z ) obtained from deltal phantom was added for the calculation of PSF ( x, y, z ) with use of the following formula. PSF ( x, y, z ) = PSF ( x, y ) • LSF ( Z ) = LSF ( x ) • LSF ( y ) • LSF ( z ). The precision of the obtained LSF and PSF were evaluated by phantom experiment with computer simulation using following equations. I ( x ) = LSF ( x ) * O ( x ). [equation]. The precision of the measured PSF ( x, y ) was evaluated to be a good approximation for the image of the blood-vessel phantom. The results propose the method for the evaluation of the precision of measured point spread function. At the same time this results suggests the method of the calculation of the CT image affected by spatial resolution.