But that's not stopping the 17-year-old from Liaoning province from chasing his dream of competing in the 2016 Paralympic Games to be held in Rio de Janeiro, Brazil.
Sun lost both his arms to a high voltage power line when he was just five.
He said, "Just like any athlete, my dream is to qualify for competitions and win medals. I'm not here for fun. Everything we do is for our ultimate goal."
"I'm here because I want a better future. I'm working towards qualifying for the biggest competitions. And the Paralympic Games is definitely the biggest," he added.
Sun is currently training at the Yunzhinan Swimming Club in Yunnan, China -- where aspiring Chinese athletes train to become the best in the world.
He is coached by the same coach who trained Qian Hongyan — the leg-less girl who's aiming for gold in swimming at the 2012 Paralympic Games, which begin this week in London.
Five athletes from Singapore will be competing at the Games -- namely swimmers Yip Pin Xiu and Theresa Goh, sailors Jovin Tan and Desiree Lim, and boccia athlete Nurulasyiqah binte Mohammad Taha.