Abstract:The relationship of competitive ability and productive performance between land race Monkhead and modern variety 8275 of spring wheat in semi-arid area of Loess Plateau was invested using de Wit replacement series. It is shown that the modern variety 8275 was more productive than the land race Monkhead when planted in monoculture, but when sowed in mixture the modern variety 8275 will be eliminated in a few generations. There is a kind of negative correlation between competitive ability and productive performance in crop varieties. The reason might be that the land race allocates more resources to the vegetative organs than the modern variety of spring wheat, thereby conferring a higher competitive ability on it.