The Jiaojia site is the earliest city in the Haidai area of China, about 5000 years old. To obtain more accurately the beginning and end of this site, radiocarbon accelerator mass spectrometry (14C AMS) measurements, along with stable carbon and nitrogen isotope data, were collected from 13 bone samples. According to the measured dates, human diet was dominated by C4-based plants, and the Jiaojia site appeared before 2900 BC.