The male passenger, aged 42, who was travelling with his wife, was later placed in detention for 10 days for his "mistake", Xinjiang's local news portal iyaxin.Com said.
The man and his wife were on a flight on Saturday from an airport in Urumqi, the capital city of Xinjiang, travelling to Zhengzhou, in Henan province.
He pulled the handle to unlock and opened the door as the Urumqi Airlines plane was preparing for take-off.
He said it was his first time that he had sat next to an aircraft's security door and had been shocked to find the door had swung open.
Crew on flight UQ2505 quickly alerted police, and the man was taken away for questioning. The flight was delayed for about half an hour, the Hong Kong-based South China Morning Post reported.
It is the latest in a string of incidents involving mainland Chinese passengers opening emergency exits as aircraft prepare to take off.
He was quoted as saying, "This door is not important", when asked by airline staff why he had opened the door.
In December, a first-time traveller opened the emergency exit of a Xiamen Air passenger jet to "get some fresh air" just before it was due to take off.
