Pot experiment was conducted to determine the response of vitamin C (VC) content in tomato fruit to soil water condition at different growth stages. Growth stages were divided by the law of tomato development and the growth of the first cluster fruits, including seeding, flowering, fruit early growing, inflation and quality formation stages. Five levels of soil water condition were set at each stage, and quadratic general composite rotatable method with five factors was used. Mathematical model between VC content and soil water content of different stages was established. The main effect, single effect and coupling effect of two factors were analyzed, and model optimization was operated in DPS 3.0. Results showed that the influence of soil water content at quality formation stage on VC content was top-drawer, seeding stage was ranked the second and flowering stage was taken the least. When other stages’ soil water content was (70%~80%)θf , with the increase of soil water content at seeding or flowering stages, VC content in tomato fruit was varied slightly (variable coefficients were 2.46% and 3.08%, respectively), while a downwards parabola change was found when soil water content was risen at other three stages. Additionally, the peaks of parabola were 24.10mg/(100g), 24.21mg/(100g) and 24.10mg/(100g) when soil water contents were (67.79%~77.79%)θf, (65.58%~75.58%)θf and (68.86%~78.86%)θf, respectively. There were significant coupling effects of two factors on tomato VC content, both positive and negative. VC content might reach the highest level of 30.10mg/(100g) when soil water content at five different stages were (50%~60%)θf, (90%~100%)θf, (50%~60%)θf, (80%~90%)θf and (70%~80%)θf, respectively, while yield was decreased sharply. Tomato yield and VC content in fruit acquired desirable level, which were 996.75~1037.99g/plant and 25.40~26.02mg/(100g) when soil water contents at five stages were (90%~99.9%)θf, (90%~99.8%)θf, (90%~99.6%)θf, (74.0%~81.8%)θf and (74.3%~82.5%)θf , respectively.