Thymopentin plays an important role in improving imbalanced immune systems of patients, however, it has a limited half-life in plasma. To get more stable and active thymopentin analogs, a fusion thymosin ${alpha}1$-thymopentin ($T{alpha}1$-TP5) gene was synthesized and cloned into vector $pGAPZ{alpha}A$. $T{alpha}1$-TP5 fusion peptide was expressed in pichia pastoris and purified by metal chelating chromatography and gel filtration chromatography. The circular dichroism spectra (CD) indicated that the secondary structure of $T{alpha}1$-TP5 fusion peptide is dominated by a-helix and random coil. In vitro analysis showed that the plasma half-life of $T{alpha}1$-TP5 fusion peptide is $140{pm}14;min$, which is longer than that of TP5 ($5.6{pm}0.7;min$) and $T{alpha}1$ ($127{pm}11;min$). The in vitro activity assay presented that $T{alpha}1$-TP5 fusion peptide has greater activity in promoting proliferation of Kunming mouse splenocytes, and in vivo experiment it showed better activity in promoting the phagocytosis of macrophages and secretion of IL-2 than both $T{alpha}1$ and TP5. Our findings suggest that $T{alpha}1$-TP5 fusion peptide might be a potential therapeutic agent.