As a critical enzyme in secondary metabolism of plants, especially in the first reaction of the biosynthesis of L- phenylalanine, Phenylanlanine ammonialyase (PAL,E.C.5.3.1.5) has significant biological meaning and strong ability against bacteria. The distribution, molecular structure, enzymatic characters and mechanism of PAL in plants were reviewed. Meanwhile, the regulation mechanisms of PAL was introduced using enzymology and molecular biology. The development of the researches on molecular biology of PAL at the gene level was prospected to provide basic data for the application of PAL in fruit tress disease resistant.