To develop a nano-lithography system based on scanning electron microscopy, a high-speed and high-precision deflection system including two prelens magnetic deflectors is introduced in this article. Best length ratio between two deflectors is achieved. which attributes to high sensitivity without loss of resolution. Some trade-off has been taken between aberrations and landing angle to get optimum performance of deflection system. The art of wire electron discharge machining is used to guarantee geometric accuracy and lower inductance. Frequency response test and lithographic experiments confirm the design. (C) 2004 American Vacuum Society.