Monascus purpureus M1 with stable yield of Monacolin K preserved in the Beijing Engineering and Technology Research Center of Food Additive, was used as the starting strain, the effects of nicotinamide addition on the secondary metabolites of Monascus were investigated by ultraviolet visible spectrophotometry, ultra-high performance liquid chromatography and real-time fluorescent quantitative PCR. The results showed that the yield of red, orange and yellow pigments in the experimental group was lower than those in the control group, and the yield of Monacolin K increased 31.34% to 124.23mg/L. Electron microscope observation showed that the degree of folding of spore head and mycelium in the experimental group was significantly higher than that in the control group. Real-time fluoresent quantitative PCR showed that the expression levels of mokA, mokB, mokC, mokD, mokE, mokF, mokG and mokH genes related to the yield of Monacolin K were up-regulated, while the expression level of mokI genes was down regulated. Nicotinamide was used as additive in the experiment, and the results were expected to provide reference for the optimization of Monascus culture medium and the screening of high-yield Monacolin K products.