Abstract: Order to increase the yield of monacolin K by liquid fermentation of Monascus,the culture medium of Monascus Purpureus M1 was optimized. In this study,we added yam powder,orange peel powder,yeast,yeast supernatant,yeast lysate,wall-breaking yeast,leucine,glutamic acid and ethanol into the original culture medium. The yield of secondary metabolites of Monascus Purpureus M1 were determined in different medium. The results showed that the effect of adding glutamic acid on monacolin K production was the most significant(p<0.01)and increased by 5.60 times. The yield of monascus red pigment value and monascus yellow pigment value were imprvoed by adding yam powder,yeast,yeast supernatant,yeast lysate and wall-breaking yeast. Among these additives,the wall-breaking yeast showed the most significant(p<0.01)effect on the monascus red pigment production,which was increased by 51.4%. The morphological differences between the glutamic acid medium and the original medium were observed by scanning electron microscopy. The results showed that the mycelium swelled markedly and the gap between cell wall and protoplast was enlarged by adding glutamic acid. It was speculated that the monacolin K accumulated in the cell were transferred to the outside of cell due to the increase of the membrane permeability. At a result,the yeild of monacolin K in the fermentation broth.