Abstract: In this paper, 16 explosive cyclones over Atlantic and Pacific oceans are analyzed. The "weak" and "strong" explosive cyclones are diagnosed and compared. It is found that the basic fields are different at many aspects. The formation of strong explosive cyclones is related to the non-zonal upper jet of anticyclonic curvature. The jet can cause the upper divergence fields and baroclinity and baroclinic instability as well as the development of internal gravity waves northward. The warm advection and diabatic heating can increase the curvature. In general, when the larger value centers of potential vorticity move toward the centers of explosive cyclones, it is advantageous to explosive cyclones.