Abstract: The studies in this paper have.showed that before and after several moderately strong shocks in Ningxia, the strikes of P (main pressure stress) axes have changed distinctly, deviating from the strikes of P axes in normal structural stress field or drawing no conclusions. The longest anomaly before earthquakes can last as long as 4 years. So it is obvious that the variation before shocks can be a significant clew for the moderately strong earthquakes prediction.