Weed control is one of the major constraint factors in crop production around the world. Field experiments were conducted during 2008-2009 under intercropping systems involving alfalfa (Medicago sativa L.), sweet potato (Ipomoea batatas [L.] Lam.), peanut (Arachis hypogaea L.), and sunflower (Helianthus annuus L.) in maize (Zea mays L.) without any weeds control methods taken. The results demonstrate that maize||sunflower is most effective on weed suppression and that it also has a more competitively inhibitory effect on Xanthium compared with the other patterns by evaluating the Xanthium density and dry weight under different intercropping systems with maize. Maize||peanut, maize||alfalfa and maize||sweet potato intercrops have no apparent inhibitory effect on weeds. To further investigate the effect of maize||sunflower on weed control, indoor pot experiments were conducted by determining the effect of extractions on germination rate (GR), root vigor, MDA (malondialdehyde), SOD (superoxide dismutase) and POD (peroxidase) content of Xanthium. The results better prove that maize||sunflower extractions have more significant inhibitory effect on GR and young root vigor of Xanthium than maize monocrop extractions.