Pi3 waves (1.67-6.7 mHz) are in the same frequency band as Pc5 waves but have an irregular wave form, are usually thought to be induced by ionospheric currents, and are associated with geomagnetic substorms.Magnetic recornection is the most important way to transport energy and mass from solar wind into the magnetosphere, and is usually controlled by the IMF Bz component.Here we show evidences that magnetic reconnection occurred around the southern cusp when the IMF was dominantly towards negative GSM x direction.The SuperDARN observations indicated the magnetic reconnection indeed occurred near the southern cusp.The magnetic reconnection made an electromagnetic perturbation imposing on the ionosphere current near the cusp and then induced a Pi3 pulsation.The accompanied electric field mapped to low latitude and the equator at a speed of~125 km/s through the waveguide formed by the ionosphere and the ground and also mapped to the high latitude in the northern hemisphere along the magnetic field lines.The nearly in phase on the H components and out of phase on the D component support this mapping processes.The wave amplitude generally decreased with decreasing latitude but the parallel component was only significant in the southern hemisphere, suggesting again the Pi3 wave generating in the high latitude in the southern hemisphere and only the transversal component can efficiently map to the northern hemisphere via the field lines.The parallel component of the Poynting flux vector seen by Cluster near the exterior southern cusp was directed away from the ionosphere, strongly supporting the wave was originated in the ionosphere below.