The story of "Boxing King" begins with the guest role of Patrick Tam, who plays a boxer and Lai Yiu-cheung as his coach. In a boxing match, Patrick Tam was seriously injured due to Lai Yiu-cheung's mistakes in coaching. Later, in a beating incident, Patrick Tam was unable to fight back due to his injuries and was beaten to death. Cheung Chun-long plays the younger brother of Patrick Tam. When he learned that his brother's death was related to Lai Yiu-cheung, he had an argument with him, and Cheung Chun-long was imprisoned for the dispute. Ten years later, Lai Yiu-cheung has become a boxing legend with many fitness chains, while Cheung Chun-long, who has just been released from prison, is a handyman who can do nothing. In order to seek justice for his brother, Cheung Chun-long decided to fight for a place in the boxing world as a new boy who knows nothing about Muay Thai and challenge the boxing giant.