Abstract: In this investigation, using a two-dimensional particle code, we have exploredthe influence of the fast flows in plasma sheet on the triggering of substorms. Wehave found that, the local speedy flows in plasma sheet could trigger the magneticreconnection process and cause the fast release of magnetic energy stored in mag-netotail. However, continuing, stable and homogeneous fast convections in plasmasheet may depress the magnetic reconnection processes in magnetotail. The resultsobtained in this study indicate that the local Bursty Bulk Flows(BBFs) can lead tothe onsets of magnetospheric substorms; nevertheless, when the IMF keeps south-ward for a long time, there may be no substorm onset, which has been called SteadyMagnetospheric Convection processes.