According to the requirements of optical fields for metal micro devices with higher aspect ratios,a metal micro-grating with the high aspect ratio was fabricated on a metal substrate by using the UV-LIGA technology.The “exposure step by step” and “development once” were used to fabricate a SU-8 thick photoresist mold with high aspect ratio to overcome the technologic difficulty in fabrication processing.For the defects of electroforming layer caused by long operation time,the fractional electroforming and other methods were adopted to obtain the electroforming grating structure..At the same time,the line width compensation method was taken to solve the problem that line width of SU-8 photoresist mold was reduced by swelling.In the process of stripping photoresist after electroforming,the ultrasonic method and soaked method were alternately used.Finally,the metal micro-grating with a period of 130 μm,and a size of 900 μm×65 μm×243 μm was fabricated.The high aspect ratio of the metal micro-grating reaches 5,and its relative error on overall dimensions is lower than 1%.Moreover,the surface roughness of metal micro-grating is lower than 6.17 nm.This research breaks the height limitation and substrate fragile of the exciting fabrication methods for metal micro-gratings with high aspect ratios.