Abstract: Pore pressure prediction ahead of bit is very important for selecting reasonable drilling measures and ensuring drilling safety in the well drilling process.However,the existing methods for formation prediction ahead of bit all have shortcomings,making it difficult to achieve prediction accuracy required for field operation.Through analysis of the relation between seismic interval velocity and pore pressure,a modified Fillippone pore pressure prediction method ahead of bit with seismic interval velocity was proposed,and the determination methods for rock matrix velocity vmax and correction parameter n were also presented.Firstly,the parameters in the model were initialized according to the region geological information and the data of drilled well.Then the acquired pore pressure data and drilling fluid density data while drilling were incorporated into the model as the constraint and made it possible to update the parameters in the model in real time.Thereby,pore pressure prediction accuracy was improved.The proposed method has been applied to certain wells in Junggar Basin in Xinjiang Oilfield and the relative error of pore pressure prediction was less than 10%.Compared with the traditional methods such as trend line method and Fillippone method,this method was much higher in prediction accuracy.In addition,field application showed the method to be scientific and effective,and could meet the needs of safety and technical requirements.