Abstract: The precision and resolution of the solution of the ART technique which is used toin verse the velocity structure on the north part of the North-South seismic belt based on the pn travelling time have been discussed in detail, The two main factors involved in the observation date that could effect the above result have been analysed and the ways to overcome these problems have been suggested. The limited criterion of the resolution is 25KM for Pn-waves. The optimum choice of the grid size should be 35-55KM under the condition of the resolution and the covariance well -matched, The resolution matrix and covariance matrix corresponding to the solution have been computed, The conclusion given in another paper is directly supported by these results.