Abstract: The electro-hydraulic servo valve is a key component of the hydraulic servo system, and the machining quality of the main valve hole is the core factor for ensuring the performance of the electro-hydraulic servo valve. Its parts require high dimensional accuracy, small surface roughness of the inner hole, and the machining difficulty is very high. Starting from the actual production needs, the author of this article has conducted extensive research and testing on the processing technology of servo valve main valve holes, and designed a process method for processing the main valve holes through using the conventional machine tools. After practical use on multiple oil drilling and production automation machines, it has been proven that the performance of the main valve holes processed by the process method described in this article is stable and reliable, fully meeting the needs of high-precision position control hydraulic servo systems.