Abstract: In order to improve the content of lovastatin produced by the fermentation of Monascus purpureus M21, the optimal mutagenesis dose of single mutagen such as ultraviolet ray, nitrous acid and lithium chloride was firstly determined, and then the complex mutagens of ultraviolet ray-nitrous acid and ultraviolet ray-lithium chloride were used to mutagenize the original strain M21. The results showed that the optimal treatment dose was the irradiation time of ultraviolet ray being 90 s, the treatment time of nitrous acid being 30 min, and the concentration of lithium chloride being 0.8‰. The complex mutagen of ultraviolet ray and lithium chloride had better effect on the complex mutagenesis of the original strain M21 under the optimal treatment dose, and the three high-yield mutant strains ULi17, ULi19 and ULi26 were obtained. The production of lovastatin was 75.2%, 60.4% and 67.0% higher than that of the original strain, respectively. The results of genetic stability showed that ULi17 had the highest yield and stable genetic characters, so ULi17 was identified as the original strain for the subsequent studies.