Abstract: Accurate pore?pressure prediction in overpressured regions is essential to ensure safe drilling operations，also provides essential data for reservoir planning and reserves estimation. Based on the differences of petrophysical signatures between different overpressure mechanisms，the prediction method for overpressure generated by fluid expansion mechanisms was syudied. The results showed that the Eaton method is suitable for estimating overpressure generated by different mechanisms. Taking Bonan sag of Zhanhua depression in the Jiyang subbasin as an example，the procedure of determining the exponent c and predicting fluid pressure by Eaton method were explained.At first，it is initially identified that the exponent c was between 1 to 4. Then，introducing a parameter the sum of the squares of relative error and using the iterative method，the exponent c could be determined by comparing the different sum of the squares of relative error. The results showed that the sum of the squares of relative error was the smallest when the Eaton exponent is 2.6，and the prediction was most accurate