Abstract: In this paper, the computer algorithm of the ray tracing in a sphyerically asymmetric and locally quasi parabolic electron density model is presented. The property curve of the variation of the group time-delay with the take-off angle is analyzed. The limitations of the traditional algorithm used in obtaining the minimum group time-delay is pointed out, and discussed of the correlation of the property curve with the backscatter ionogram are made. Properties of the power distribution on the backscatter ionogram is also discussed.