Grating-based X-ray imaging system is an important tool to investigate the inner structure of thick samples. The key components of the system consist of three golden gratings. The high aspect ratio gratings are fabricated using the SU-8 material. Considering the grating linewidth broadening varies with exposure dose, the relationship between linewidth broadening and exposure dose is studied experimentally. A series of gratings with different periods and different duty cycles are designed by optimizing the linewidth and exposure dose. Finally, the gratings are successfully fabricated by combining UV lithography and electroplating.