Polynyas play an important role in climate change with an efficient exchange of heat and matter between the atmosphere and the ocean in polar regions. This study investigated the influence of strong tides and atmospheric forcing on the Amundsen Sea Polynya, especially focusing on large-area polynya events from 2002 to 2020. We found that the geographical locations of the polynyas are closely related to the underwater ridge, where tidal currents are relatively strong. More importantly, strong cross-ridge winds are the “triggers” above the sea surface for the initial formation of the Amundsen Sea Polynya, while strong tides under the sea surface tend to create large-area polynya. Four of the five largest polynya events occurred mainly during spring tides. Only the 2016 event occurred during the normal tide period, which was atmosphere-dominated. Strong tides significantly affect the evolution of polynyas by strengthening the vertical mixing of seawater. Given that ocean in Antarctica might become warmer, tidal mixing might enhance the mixing in the future climate.