In order to screen out YAC clones in the CEPH YAC library related to a definite gene, DNA fragment or locus, we need to establish a screening system. This paper includes the establishment of this system and the evaluation of its feasibility. According to the experiments, we suggest that it is better to screen the Mega YAC part of the library at first and put five culture plates as a group. Meanwhile, FISH experiments to assess the quality of CEPH YAC library and the first generation physical map of human genome, Were conducted FISH experiments on 26 YAC clones were carried out. There were 13 clones that were chimeric (about 50%), 6 clones that were mapped by mistake (about 23%). So, there were only 9 clones that were mapped correctly and were not chimeric (about 35%).