Abstract:Abstract: As an effective method to strengthen gene expression in genetic engineering, the multi-copy strategy has gained increasing favor among molecular biology researchers. This strategy includes three ways: multiple-copy of expression cassette, multiple-copy of target gene and multiple-copy of promoter. They are widely applied in genetic engineering and there are five methods to achieve multi-copy, including random series connection, PCR series connection, the joints connection, isocaudarner series connection and chemical synthesis. Multi-copy strategy is one of the approaches to improve particular protein yield by means of molecular biology and its feasibility has been proved in many studies. Adding the strategy to genetic engineering will make the genetically products more suitable for industrial production.