Abstract: In the course of long-termed mutual effect and co-evaluation with pathogen, plants bring about a series of defensive systems, so as to effectively avoid being infected by pathogen. When being infected, local cells in the infectious part usually die in several hours, which restrict pathogen from propagating or spreading. The above phenomenon is called Hypersensitive Response, HR. The resistance that the whole plant works several days or one week after producing HR and that aims at other pathogens is called Systemic Acquired Resistance, SAR. SAR emphasizes on plant’s ability to acquire integrated resistance. According to lots of research, SAR is ubiquitous and universal. Many studies confirm that, SA is an important induced factor of SAR, and is an important part of the signal conduction path by which plants activate a series of defensive feedback after it is infected by pathogen. In this paper, the author elaborated on the effect of SA exerted when inducing plants to produce resistance and the study progress of it. In addition, the effects of SA in other respects referring to resistances were also introduced briefly in this paper.