In order to evaluate the effects of cover crops on reduced weed biomass in hybrid sunflower an experiment was carried in the research stations, Natural Resources Medicinal Plants (Samian_Ardabile) with 3 replicates in 1390-1391. The first factor was considered three type of cover crops, winter rye, spring barley, winter wheat with 2 control treatment, second factor was mulch management at two levels (living mulch, dead mulch) and the third factor was two cover crops planting date (synchronic with sunflower planting, 45 days after). Results showed interaction (cover crop×planting date), had a significant influence on annual weed biomass. Convolvulus arvensis biomass was influenced by cover crops at level probability of 1 %, also hragmitesaustralis biomass was influenced by cover crops and planting dates. Simultaneous planting dates, cover crops with a sunflower had greater role rather than 45 days late in reducing weed biomass. Then the control 1 was found at wheat cover crop treatment, the maximum seed dry weight with average of 176/49 gram per square meter.