Abstract: PAL, a critical enzyme in secondary metabolism of plants,was the first and key enzyme of the phenyl propanoid sequence.It has great influence on plant physiological function.In this paper,the PAL’distribution,separation and purification,basic characters,three-dimensional structure, mechanism were reviewed. Meanwhile, the progresses of the research on PAL in secondav metabolltes were especially emphasized, in order to enrich the mechanisms of regulation to secondary metabolism,and provide some references for its advanced research..