In order to obtain a large amount of corn glutaminase with biological functions， the recombinant plasmid pPIC9K-TGase was first identified by double enzyme digestion and PCR using molecular biology techniques， then linearized by Sac I， electrotransferred into Pichia pastoris GS115， and its expression was induced by 1% methanol. Results by SDS-PAGE analysis， compared with the control， there was a specific protein band at the molecular weight of about 60 ku， which was the target protein. Then， the yeast expressed TGase was reacted with 0.2% casein solution for 2 hours， and SDS-PAGE showed that casein was polymerized into polymers with different molecular weights， indicating that the expressed protein had a good cross-linking effect on casein. Moreover， the TGase from yeast expressed was added to yogurt， and it was observed by scanning electron microscope that the yogurt network structure with yeast expressed TGase became relatively dense. Conclusion: The yeast expressed glutaminase has the biological activity of crosslinking milk protein.