We used Arabidopsis thaliana wild-type Col-0 (CK) and tyrosine pathway–deficient mutant sscd1 as experimental materials, observed the seeds germination and seedling growth which treated with four concentrations of phenylalanine (0.1, 0.5, 1.0, 2.0 mmol/L), and analyzed the expression of key genes HGO, MAAI and SSCD1 in tyrosine degradation pathway. The results showed that: 0.5, 1.0, 2.0 mmol/L phenylalanine could inhibit the germination and root length of Arabidopsis seedlings, and the inhibitory effect on the mutant sscd1 was higher than that of the wild type. The growth of aboveground parts of seedlings was promoted under 0.1, 0.5 mmol/L phenylalanine and inhibited under 1, 2.0 mmol/L phenylalanine, the inhibition of mutant sscd1 was more seriously. QRT-PCR found that the expression of HGO in wild type and gene expression of MAAI and HGO in tyrosine pathway-deficient mutant sscd1 was significantly up-regulated. The above results showed that phenylalanine promoted the tyrosine degradation pathway in plants.