On the basis of data of Gansu Seismological Network, the focal mechanism solutions of 31 M_L≥4.0 earthquakes which occurred in the northeastern margin of Tibetan Plateau after Wenchuan earthquake were obtained in the paper by using the CAP method, and then the results were analyzed and discussed. The results showed that because of the adjustment process of regional stress field in northeastern margin of Tibetan Plateau which was influenced by Wenchuan earthquake, activities of moderate earthquakes there presented zoning and clustering, and earthquake types had obviously regional characteristics. The maximum of principal stress azimuth of 31 moderate earthquakes revealed that predominant azimuth in Qilianshan seismic belt was NE and that in southeastern Gansu was nearly EW, which showed a localized characteristic of regional stress field.