The de Wit series experiments were conducted to study the relationship between relative competitive ability in mixture and grain yield in monoculture along four levels of soil water and fertilizer application at the experiment station of Yuzhong in Lanzhou University, Gansu Province, China. The results showed that landrace Heshangtou had greater competitive advantage than the modern variety Dingxi-24 under a series of soil water and fertilizer conditions. Although the inhibitory effect of the landrace Heshangtou on the modern variety Dingxi-24 was reduced along the soil water and fertilizer gradients, the modern variety Dingxi-24 was eventually replaced by old variety Heshangtou. At severe soil water deficit and no fertilizer application, and with sufficient soil water and fertilizer application, the modern variety Dingxi-24 had higher grain yield in monoculture than the old landrace Heshangtou (P<0.05). A negative relationship between the relative plant competitive ability and seed yield of wheat was found with severe water shortage and no fertilizer application,and with sufficient soil water and fertilizer application, i.e. the varieties with higher competitive ability had lower seed yield. Under moderate soil water deficit and intermediate fertilizer application, the old landrace Heshangtou had a higher grain yield in monoculture than the modern variety Dingxi-24, but the productive performance between them did not show statistically significant differences (P>0.05), this suggested that the old cultivar Heshangtou which had poor productive performance under severe soil water deficit and fertilizer application did not have low seed yield at moderate soil water deficit and intermediate fertilizer application. A positive relationship between the relative competitive ability and seed yield of wheat varieties was found, i.e. the variety with the higher competitive ability had higher seed yield. Under severe soil water deficit and low fertilizer application, the grain production of the old variety Heshangtou almost equaled the grain production of the modern cultivar Dingxi-24, that is a neutral relationship between competitive ability and seed yield occurred. Our results indicated that a particular relationship did not exist between competitive ability and seed yield, in other words, plant competitive ability of wheat varieties was not definitely related to seed yield. At a severe soil water deficit, no fertilization and with sufficient soil water and fertilizer application, the modern variety Dingxi-24 had higher aboveground biomass in monoculture than the landrace Heshangtou (P<0.05). When the soil water deficit was severe, the soil water utilization efficiency of the old cultivar Heshangtou was significantly lower than that of modern cultivar Dingxi-24 (P<0.05). With the change of soil water supply, the soil water utilization efficiency of the old cultivar Heshangtou was significantly increased. However, the water utilization efficiency decreased when soil water was sufficient and no longer a limiting factor for the growth and reproduction of the old cultivar Heshangtou. Therefore, the effect of soil water supply on the utilization efficiency of the old variety Heshangtou was stronger than that of the modern variety Dingxi-24. Therefore, our experimental results suggest that improving the soil water utilization efficiency to a certain extent benefited the adaptation spring wheat to a limited soil water environment.