Abstract: To express the porcine antibacterial peptide Cecropin P1 in Pichia pastoris and analyze the biological activity of the expressed product,Cecropin P1 gene was designed and synthesized to include the partiality codons of P.pastoris based on the gene sequences encoding swine antibacterial Cecropin P1.The linearized recombinant was shocked into P.pastoris X-33 by electroporation, and the high copy transformants were screened with Zection and PCR. After being pured，Tricine -SDS-PAGE showed a single bright band. Agar diffusion method was used to analyze the biological activity of the purified antimicrobial peptides under the thermal, different pH, trypsin and pepsin. The results indicated that the cecropin P1 had a strong thermal stability, acid stability and pepsin stability.However, in alkaline environment and pancreatin, the antibacterial activity of cecropin P1 decreased significantly.