Abstract: To study the nutrient requirement character of Huangyan Purple yam can provide a scientific basis for rational fertilization, as well as avoid and reduce the waste and pollution caused by irrational fertilization. Single factor randomized block design and quadratic saturation D optimum design were used to study the effect of density and NPK fertilizers on tuber yield of purple yam, and corresponding mathematical models were established. In high-yielding cultivation of purple yam, application amount of K fertilizer had the greatest and positive effect on the yield of purple yam, while N and P fertilizers had a minor and negative effect on the yield of purple yam. Thus, to control N, add K and save P fertilizers is the effective measure to obtain high yield in purple yam. The optimized planting density of Purple yam was 20-25 thousand plants/hm2, the optimum agricultural combination factors for purple yam obtaining a yield more than 27.0 t/hm2, were showed as follows: rates of nitrogen were 185.06-333.94 kg/hm2; rates of phosphorus were 65.30-189.69 kg/hm2；rates of potassium were 342.83-559.30 kg/hm2. Overuse of fertilizers to increase yields is not desirable. Instead, NPK fertilizers should be combined and soil fertility should be well managed. The quadratic saturation D optimum design can be applied to optimum fertilization techniques in Huangyan Purple yam cultivation.