A M7.8 earthquake occurred at the focal depth of 100km in the northern Peru on May 26,2019(Beijing Time). The focal mechanism and rupture process of the earthquake are determined rapidly by using the waveform inversion method with far-field body waveform data downloaded from Incorporated Research Institutions for Seismology(IRIS). The fast focal mechanism determination using W-phase method indicates that the earthquake is a normal fault-type with a intermediate-depth,which is generated within the Nazca plate as a result of internal deformation within the subducting plate. By performing finite fault slip inversion with teleseismic P waves,we find that the nodal plane(strike=349.0°,dip=61.0°)fits the data well after comparing waveform fits based on the two planes of the focal mechanism solution,and most of the rupture slips concentrated in the northwest of the hypocenter with the maximum slip of 3m. The source-time function with a duration of 70s suggesting that over 80% of the moment release occurred during the period of 40s to 60s after the rupture initiation. The concentration of rupture and the size of moment release were weak within the first 40s,then peak slip rate reached the maximum,and after 60s the rupture healed quickly.