Abstract: The influence of the addition of mucor on quality of yak mold cheese was researched to determine its optimal addition and fermentation time by the single factor experiment.In the case of the same condition, Actinomucor elegans was added at the mass ratios of 0.2%, 0.3% and 0.4%.The physicochem ical indexes such as sensory evaluation score, texture index, nutrient composition, pH value, decomposition index of protein and lipid were mensurated. The results indicated that the quality and sensory evaluation score of which added 0.3% mucor were best. With the addition of starter rising, the content of moisture, protein, lipid and pH value showed a downward trend while ash was on the rise.Mature to the sixth day, the sensory index of yak mold cheese was the best.In the process of maturation, the content of soluble nitrogen at pH4.6 or 12% trichloroacetic acid soluble nitrogen, thiobarbituric acid value, acid value increased gradually. So the optimal addition amount of starter was determined to be 0.3%.The quality of yak mold cheese was best when fermented for 6 days.