The abduction was exposed after police took the circus organizers in for investigation.
Four years ago in his hometown, Zhang, then nine years old, was tricked into joining the circus after the organizers said he could learn kung fu with them.
But the dream of running away to join a circus quickly became a nightmare.
The boy told police he only got one meal a day. The clothes he wore were those discarded by others.
Always at risk of being bitten by snakes, Zhang was forced to perform at shows in towns and cities throughout the country.
"He would get a fierce beating whenever he was unwilling to perform," officers said.
Other children who performed in the circus had a much better life as they were the children of the organizers.
Zhang was also forced to do chores such as cleaning and washing, police said.
Officers bought clothes and books for the boy who had difficulties in communicating with them after years of hard work and neglect.
But police officers managed to identify and contact the boy's parents earlier this month.
"I hope he will catch up with his studies and go to college," said Yang.
The boy's father, Zhang Qingtong, a mason, said the family adopted the boy when he was a baby.
"For most of the time we thought that we would never see him again."
In a country where children abduction is not uncommon, Zhang is one of the lucky ones.
Chinese police rescued more than 2,000 kidnapped children in 1,717 cases during a nationwide campaign against child trafficking last year.