Femtosecond (fs) laser Two-photon Microfabrication is a new real 3D microstructure fabricating method with sub-micron resolution power. In the fabricating process, some factors cause the appearance of the final microstructures different from the design figure. In order to eliminate the appearance error and improve the machining precision, in this paper, two machining defect factors are discussed and real-time in situ compensation is realized based on machine vision monitoring and pattern recognition technique. For the position error induced by the movement error of the 3D micro-displacement scanning stage and the fluid of the liquid resin, one relative distance reference mark system is built to compensate the error. Through the CCD vision monitoring system, at the beginning of every layer fabrication, the 3D scanning stage should be re-posited and ensure the relative positions to the reference marks are right. For the other defect factor, deficient exposure, with the image processing and pattern recognition techniques, the solidified degree of the resin cell can be automatically judged and re-exposure process will be done. This method decreases the accumulative error and is evidently available for the 3D microstructure with larger height value.
