There are two kinds of changes of gene expression,that is,novel gene expression and differential gene expression in quantity. Cloning technique of differentially expressed gene in quantity mainly is mRNA differential display, which is presently one of the most effective methods. However, mRNA differential display possesses higher unreal positive rate,in order to overcome its shortcoming, some novel strategies and methods were advocated,such as differential subtraction display, subtraction based on LD-PCR, LD-PCR based on subtraction,those techniques have dominant advantages to mRNA differential display.