The initial investigation found that K9017 sped into a turning point at the station, ignoring a red light prompting it to stop, and was travelling at a speed of 55 km/h (34 mph).

Passengers on the K9017 revealed that the train had initially stopped for twenty minutes before arriving at Chenzhou railway station, at around 02:00.

[6] Guangdong Railways Group, the operator of the two services, has blamed the accident on brake failure.

[5][7] An investigation was requested by Liang Jiakun, deputy director of the State Administration of Work Safety.

[7] According to a briefing held on June 30 by the railway authority and Chengzhou city government the incident was caused by the brake failure of the K9017 train.

The cause was determined as being that a dust plug of a brake house of one of the carriages was not removed at the Nanjing Puzhen factory, violating manufacturing instructions.