Yeast protein expression system is the most economical and efficient expression system among eukaryotic protein expression systems, which combines the advantages of prokaryotic expression system and eukaryotic expression system. Because of its fast growth rate, low culture cost and clear genetic background, it has been widely used in industrial microorganisms. The yeast expression system can correctly process, modify and fold post-translational proteins, so it is often used for the expression of heterologous functional proteins in eukaryotes. Among them, the Pichia pastoris expression system is more widely used. Compared with other systems, it has unique advantages, such as strong promoters FLD1, GAP, AOX1, etc., which can make the expression of heterologous proteins lasting and efficient.