A large tsunamigenic earthquake of magnitude 8.2 occurred on the Alaska‐Aleutian subduction zone in July 2021. To reveal the characteristics of the event, we first applied spectral and wavelet analyses to the induced tsunami recorded both at the local and Pacific‐wide sea level observation networks. Because the earthquake was relatively deep (∼30 km), the resultant maximum tsunami amplitudes were only ∼5 and ∼50 cm in the open ocean and coastal area respectively. However, owing to the unique geological feature of the region, the tsunami had dominant periods of 57–73 min, which are longer than that typically generated by similar‐size megathrust earthquakes. Furthermore, we compared multiple source models inferred from various data sets and evaluated their performances in reconstructing the observed tsunami waveforms. The comparison results suggest that the up‐dip limit of the rupture area must be restricted at depth of ∼20 km to accurately reproduce the observed tsunami waveforms. Shallower slips beyond the prescribed limit led to an overestimation of the tsunami amplitude. This implies that the earthquake was unlikely to rupture the plate interface on the near trench section.