The fire ripped through the bus as it traveled on an elevated road in Xiamen during Friday's evening rush, killing 47 people and injuring 34 more. It is unclear if the suspect's death is counted in the tally.
Police identified him as Chen Shuizong after an on-site investigation, interviews and examination of evidence, including DNA, a government notice said. It said Chen was a local resident born in 1954 and that police found a suicide note in his home.
He was unhappy with life and set the fire to vent his anger, the city said. Xiamen's municipal government issued the notice Saturday through state media and a Xiamen police microblog.
China has seen bombings and arsons of buses and public buildings in recent years, by people trying to settle personal scores or having overtly political grievances.
In 2009, an unemployed man set fire to a packed bus in the central city of Chengdu, killing himself and 26 others. In other case, people angry or unhappy with life have used knives or other weapons in attacks on children at schools.
In a microblogging account reported to be Chen's, the writer claimed to be destitute and pleaded for an opportunity to live. The last entries were made on Thursday, the day before the fire, when the writer chronicled his frustrated efforts to get a local police station to correct his age so he could be eligible for social security payments.
The microblogging account was removed by late Saturday.
After the fire, emergency responders found bodies piled inside the charred, skeletal bus. Investigators said early Saturday the fire appeared to have been intentionally set. State media reported gasoline traces were found, though the bus ran on diesel fuel.
Xiamen was known for centuries in the West as Amoy. It had suspended service of the entire express bus system after Friday's fire, but operations resumed Saturday morning.