The technology of genetic engineering has been widely used to express macromolecules such as enzymes. However, it is difficult to detect and purify the micromolecules such as small peptides, because of their instability and degradability. Construction of multi-copy recombinant expression plasmid can be achieved by inserting multiple target genes or expression cassette containing target genes with the same orientation into expression vector. This is effective to increase the expression level of small peptides. In this article we described four methods in order to provide some optional methods and ideas for the expression of active small peptides.