The Beaufort Gyre is one of the most significant circulation systems in the Arctic Ocean and serves as the largest freshwater reservoir in the Arctic region. Variations in the Beaufort Gyre can affect the storage and release of freshwater within it, thereby affect the freshwater export of the area to the Atlantic Ocean, thus affecting the global climate. In this study, we utilized the latest ORAS5 reanalysis data from the European Centre for Medium-Range Weather Forecasts (ECMWF) to study the variations of the Beaufort Gyre from 1979 to 2018 and analyze the mechanisms behind these variations. Our findings indicate that during the period of 1979-2018, the Beaufort Gyre expanded northwestward but is constrained by topography on the northwest side. Atmospheric circulation patterns associated with the Arctic Oscillation (AO) impact the position, extent, and strength of the Beaufort Gyre. During positive AO phases, the area and volume of the Beaufort Gyre are smaller, with its center located closer to the coast and exhibiting relatively weaker strength; during negative AO phases, the situation is reversed. The strength of the AO phase also leads to variations in the gyre's dynamics. From 1989 to 2010, the AO shifted from a gradually weakening positive phase to a strengthening negative phase, resulting in a continuous increase in sea surface height at the center of the Beaufort Gyre, along with increases in the area and volume of the gyre and an enhancement in strength of the gyre, and with an increase of the deviation between the gyre's center and its centroid. Additionally, the Arctic Dipole Anomaly (DA) can influence the variations in the Beaufort Gyre to some extent. As summer sea ice concentration in the Arctic decreases, the sea surface stress acting on the Beaufort Gyre is expected to change, potentially leading to enhanced summer Ekman pumping and subsequent accumulation of freshwater in the Beaufort Gyre region. Accompanying these circulation changes, the freshwater content and sea level interior of the Beaufort Gyre exhibit significant decadal variability, which are intricately connected to the Ekman dynamics induced by the changes in atmospheric circulation and sea ice decline.