 Born in 1887, 1898, or 1889 in Yongcheng, Henan, Sun joined a bandit gang in his youth, and eventually became a message-carrier for the Yangshan bandit chief Zhang Ping.He eventually joined the Songxian Pacification Force (SPF), an anti-bandit militia that mostly consisted of ex-bandits.Sun managed to rise to a minor command in the SPF, but he resumed banditry following the suicide of his superior Han Yukun in 1925, or after the SPF's crushing defeat at Xi'an against warlord Feng Yuxiang in 1926.