Affected by the special geographical environment, winter snowfall in Beijing is often accompanied by the easterly wind in the boundary layer. The water vapor transport and dynamic convergence effect caused by the easterly wind in the boundary layer are of great significance to the occurrence and development of snowfall. This paper is based on the topographic characteristics of the Yanqing zone of the 2022 Winter Olympic Games and is different from the existing snowfall studies on the easterly wind of boundary layer in plain areas. The paper compared the easterly wind mechanism in the boundary layer with various thermal and humidity properties and development heights on snowfall under similar weather conditions. The results show that: (1) A longer route through the Bohai Bay is beneficial to the obvious humidification of the boundary layer easterly wind and vice versa. (2) The “dry and cold” easterly wind can form a cold pad to lift the warm and humid air in the Beijing plain area. When the easterly wind develops deep in the vertical direction (over 600 m), it can overturn the Jundu mountain with lower altitudes in eastern Yanqing and form a around-flow confluence on leeward slopes. At the same time, the easterly wind is blocked by the Haituo mountain with higher altitudes in the west, forming the forced uplift of the windward slope. The two effects together lead to the convergence of the strong east and the weak west, which causes more snowfall distribution in the east than in the west. (3) The “warm and humid” boundary-layered easterly wind cannot cross the Jundu mountain westward because of its lower vertical development height, which has little effect on snow in Yanqing. (4) When the air gets affected by the northwest airflow of 500 hPa, closer to the terrain, the saturation area near the 700 hPa height and the lifting movement make the high-altitude mountainous area of Yanqing experience the obvious snowfall.