Lu Su was from Dongcheng County (), Linhuai Commandery (), which is located southeast of present-day Dingyuan County, Anhui. He lost his father not long after he was born, so he lived with his grandmother. Lu Su was very generous with his family's wealth as he used it to help the needy. Wei Zhao's "Book of Wu" () described Lu Su as having a stalwart and extraordinary appearance. He had great ambitions since he was young and was very fond of strategy.