Genomic DNA gains and losses can play a causal role in many diseases. Comparative genomic hybridization (CGH) is a powerful technique for the detection of chromosomal imbalances. CGH can also be used to identify different genes in diverse subtypes of the same species, thus indirectly confirming those phenotypes. The CGH method is based on a comparison of the test and control DNA samples which are labeled with different fluorophores, equally mixed, and simultaneously hybridized on one microarray, which can measure the DNA copy number differences between the test and control samples rapidly . CGH can be used to detect DNA copy number alterations in entire genome which can help determine the abnormal development of cells, and can provide an important means for diagnosis of tumors and other diseases related to chromosomal alteration. When applying CGH to tumor genetics, an entire genome “scanning image” can be obtained and the gains and losses of tumor DNA in a whole genome can be recognized: tumor suppressor genes may be lost or oncogenes may be amplified.