Han Dang was from Lingzhi County (), Liaoxi Commandery (), which is in present-day Qian'an, Hebei. He possessed great physical strength and was highly skilled in archery and horse riding. The warlord Sun Jian recognised his abilities and recruited him. Han Dang accompanied Sun Jian on his military exploits throughout the 180s until 191, from the Yellow Turban Rebellion to the campaign against Dong Zhuo. He was hardworking and made many contributions in battle. However, even though he was serving in an army, he was actually more of a "youxia" or mercenary, so he was not awarded any titles for his achievements. He remained as a Major of Separate Command () under Sun Jian.