Abstract: The complicated MEMS are assembled by many micro-machinery parts.As traditional metal cutting technology,there is tolerance in the micro-machinery fabrication.It is very important to give the part tolerance especially when there are assembling relationships between the micro-machinery parts.As the micro-machinery fabrication technology is different from traditional fabrication technology,the determining and marking method of tolerance is different too.The tolerance of micro-machinery part based on LIGA（Quasi-LIGA）technology was studied in the paper.In the process of LIGA（Quasi-LIGA） fabrication technology,the tache,reason,law and scope in the special fabrication condition of part tolerance were analyzed.Based on the analysis,the determining method of micro-machinery part dimension was given.