The accident took place when the seaplane from the Beihai Fleet was conducting a flight drill above the Jiaozhou Bay near Qingdao City in Shandong Province, state-run Xinhua news agency reported.
The fate of the pilot was not known, the People's Liberation Army Navy (PLAN) said.
Rescue was underway, the report said.
Last month, two Chinese pilots were killed when a frontline Su-27 fighter jet also crashed in Shandong Province.