The city's name in Chinese (三门峡) means "The Gorge of Three Gateways" and is derived from two islands that split the Yellow River into three parts.

According to Chinese mythology, Yu the Great used a divine axe to cut the mountain ridge three times, creating the Sanmenxia gorges to prevent massive flooding.

Archaeological finds near Sanmenxia between 1956 and 1991 revealed mass chariot graves and bronzeware of Western Guo State rulers.

Sanmenxia is located in western Henan on the southern (right) bank of the Yellow River, and is surrounded on three sides by mountains, with elevations generally increasing from northeast to southwest.

Monthly daily average temperatures range from −0.3 °C (31.5 °F) in January to 26.4 °C (79.5 °F) in July, and the annual mean is 13.9 °C (57.0 °F).