The manufacturing process and defect types of graphite materials are introduced in this paper, combining with the working characteristics of the liquid rocket engine face seal, the necessity of testing the internal defect of graphite material for face seal is expounded. A comparative analysis is made on the present nondestructive testing methods, the X-ray detection method is the best for liquid rocket engines face seal. The key parameters of the X-ray detection such as gray scale, contrast, voltage, current, filter slice and integral time are compared and analyzed, then the process parameter setting rule and the high precision detection method of the internal defect inspection of graphite material are confirmed.And a visual simulation analysis of the internal space of graphite material is realized.And method for calculating the rate of porosity of graphite materials based on image processing.Finally the characteristics of graphite material internal defects typical of standard samples input forward of liquid rocket engine face seal are established.