Using a pot experiment and quadratic orthogonal regressive rotation design with four factors,the effects of irrigation amount and fertilizer rates of nitrogen,phosphorus and potassium on vitamin C content in tomato were investigated.A model of regression relationship between water and fertilizer mounts and vitamin C content in tomato was established.Single and coupling effects of all four experimental factors were studied.The results showed that for the soil and tomato variety used in the experiment,if other factors were zero codes,the relationship between vitamin C content and irrigation amount,P fertilizer rates could be estimated with a second degree parabola,which was open downward,while the second degree parabola between vitamin C content and K fertilizer rates was open upward,but vitamin C content was not affected by N fertilizer.The interaction between irrigation amount and P fertilizer rate,between N and K fertilizer rates showed a negative effect.It was indicated that supplying the fertilizers of P,K,or irrigation amount properly could raise the vitamin C content in tomato effectively.However,N fertilizer rate restrained significantly the accumulation of vitamin C in tomato by the negative interaction between N and K fertilizer rate.