Systematic Acquired Resistance（SAR） of plant is one kind of Induced Acquired Disease Resistance,a new resistance which built in plant after being infected.Salicylic acid（SA） is an important signal molecule of SAR and transcription factor "NPR1" is activated through the signal transduction by SA.On the other hand,NPR1 is also a negative feedback regulation factor of the SA synthesis.NPR1 interacts with down-stream transcription factor "WRKY" and "TGA".Pathogenesis-related proteins are induced and expressed by the regulation of "WRKY" and "TGA",and SAR is built in plant finally.There are complicated positive regulation（negative regulation） balance relations among SA,ABA and JA,so the success activation of SAR will be interfered by these interactions.