Lü Meng was from Fupo County (), Runan Commandery (), which is located southeast of present-day Funan County, Anhui. His family migrated to the south of the Yangtze River when Lü Meng was young. Lü Meng lived with his brother-in-law, Deng Dang (), who served as a military officer under Sun Ce. When he was 14 or 15, he secretly followed Deng Dang to the battles against the Shanyue tribes. Deng Dang was shocked to see his teenage brother-in-law in battle, so he scolded Lü Meng and warned him to stop. Lü Meng refused to listen so Deng Dang told Lü Meng's mother about this. When she wanted to punish him, Lü Meng said: "It is difficult to survive in poverty. If we can prove ourselves through hard work, then wealth will come eventually. How can we catch the tiger cub if we don't enter the tiger's den?" Lü Meng's mother sighed and let him have his way.