Switching Mechanism At 5' end of the RNA Transcript (SMART) is a technology used in biology researching, So far, there is no review only about SMART technology. So, this review tries to investigate the research developments of principles, methods and applications of the SMART technology. Based on some researches and combined with the review of the related literature at home and abroad, the authors analyzed and evaluated the latest development of the research on SMART. As the applications of the SMART technology expand in many fields day after day, it has been proved that the SMART technology is a very useful and efficient skill to construct full length cDNA library. As more and more researchers know this technology, the advantages of the SMART technology become obvious, and meanwhile the disadvantages of the SMART technology also show up. That is to say, the technology needed to be improved.