Abstract: When using focused ion beam to prepare quartz glass planar TEM samples with through nano pores, problems such as high hardness, poor conductivity and excessive thickness of sample pieces would occur. By changing the tilt angle during U-cut separation of the sample, the sample sheet could be quickly cut off, separated and transferred under the low processing beam current, avoiding the drift damage to the sample during processing, or the reverse deposition phenomenon due to long processing. The prepared through nano porous quartz glass planar TEM sample had uniform contrast and less damage. The method laid a foundation for further studying the influence of laser etching on the structure of quartz glass, and also provided a technical reference for preparing planar TEM samples of similar materials using focused ion beam.