Abstract: The variation of interspecies competitiveness, and its effects on the production performance of four intercropping treatments alternating alfalfa (Medicago) and maize (Zea mays) were investigated in a 2∶2,3∶2,4∶2,5∶2 design with three replications, and intercropping area rates of 33%∶67%, 43%∶57%, 50%∶50%, 55%∶45%, respectively. Maize and alfalfa as the monocultures were the control groups. Dry matter yields of different treatments were measured, and land equivalent ratio (LER), aggressiveness (A), and relative crowding coefficient (RRC) were introduced as indexes to evaluate the interspecies competition in each treatment. In the first year of establishment, yields of all the intercropping treatments were lower than that of the maize monoculture, but higher than that of the alfalfa. The 5∶2 treatment had a better production performance and economic returns than the other intercropping treatments. In the second year, alfalfa had a high-yielding period, and occupied the dominant niche for the whole growing stage in the intercropping systems. Total biomass of all the intercropping systems were not less than the maize or alfalfa monocultures. The 5∶2 intercropping treatment had the best productivity and economic returns.