Th0 cells differentiate into Th1 or Th2 depending on multiple transcription factors acting on specific time points to regulate gene expression. Th17 cells, a subset of IL-17-producing T cells distinct from Th1 or Th2 cells has been described as key players in inflammation and autoimmune diseases as well as cancer development. In the present study, 66 patients with gastric cancer were included; the expression level of Th1- and Th17-related IFN-γ, IL-17, T-bet, RORγt in gastric cancer tissues and peripheral blood mononuclear cell (PBMC) were detected, analyzed the relationship between Th17 or Th1 infiltration and metastasis and explored the possible mechanism. Our results showed that IL-17 and RORγt expression were significantly increased in gastric cancer tissues and PBMC, especially, in metastasis patients; plasma IL-17 also increased; furthermore, the mRNA and protein levels of IL-1β, IL-21 and TGF-β were up-regulated. All the data indicated that Th17 was infiltrated the cancer tissue; IL-1β, IL-21 and TGF-β were also involved in gastric cancer development by promoting Th17 cell generation. From the above data, we speculated that Th17 cell expansion in gastric cancer may contribute to cancer development and metastasis.