Abstract: Abstract：Construction of genomic libraries is basic and important. Because traditional methods of constructing genomic libraries are very fussy and produce high background, we improve the traditional methods to solve these disadvantages. Two EarI sites are chosen as the cloning sites, which produce variable 3-base cohesive ends, so the two overhangs can be devised to prevent a match and to avoid self-ligation of vector. Genomic DNA is cleaved partially with Sau3AI and subsequently incubated with dGTP and Klenow fragment of DNA polymerase I.，so the self-ligation of fragments and ligation between them are blocked. In this study, the ARS probe vector (pHBM803/Trp) based on the improved method is constructed and then we construct the oryza sativa genomic library with the traditional method and improved method and compare them. The result of experiment indicates that the improved method can optimize the quality of library.