Abstract: The effects of nitrogen, phosphorus and potassium on yield and quality parameters of onion (Allium cepa L) were studied with the design of three factors and quadratic saturation D-optimal regression (310). According to the data obtained, a mathematical model was established, in which N, P and K were independent variables and onion yield and quality parameters were dependent variables. The model analysis showed that N, P and K significantly influenced onion yield and quality parameters, with P having the biggest effect followed by N and K. When N, P and K reached 430.7, 449.5 and 1152.7 kg/hm2, the marginal yield was 0. The interactions of N, K and N, P for onion yield were significant, with the biggest interaction area being N at 240.0#8722;720.0 kg/hm2, P2O5 at 250.0#8722;500.0kg/hm2 and K2O at 600.0#8722;1500.0 kg/hm2. In this experiment, when the fertilizer rates were N at 294.0#8722;480.6 kg/hm2, P2O5 at 332.8#8722;388.5 kg/hm2 and K2O at 861.8#8722;1119.8 kg/hm2, yield reached 75t/hm2 and quality grade passed 90. The most suitable ratio of N: P2O5: K2O was 1:0.93:2.56.