This study was carried out at the research farm of Agriculture Faculty, Bu- Ali Sina university, in 2009, to evaluate the effect of winter cereals as cover crops on weed control, improving soil fertility, yield and yield components of potato. The experiment was a randomized complete block design with three replications. The trial including seven treatments consisted of no cover crop, rye, barley and triticale, each with common and triple plant density. The results showed that rye and barley with triple plant density produced 1503.5 and 1392.2 g/m2, respectively. Rye, barley, triticale with triple and rye with common plant density reduced winter weeds biomass 97, 96, 93 and 89 percent respectively, compared to control. Cover crop treatments showed different abilities to weed control in potato growth period (15, 45 and 75 Day After Germination) compared to the control treatment. The treatments, of rye and barley with triple and rye with common plant density had the most inhibition effects on summer weeds. Soil physical properties were affected significantly by cover crops, so rye, barley and triticale with triple and rye with common plant density, increased organic carbon 26, 25, 21 and 25 percent, respectively compared with the control treatment. Rye and barley with triple and rye with common plant density, decreased soil specific weight 6.6, 7.5 and 7.4 percent, respectively compared with the control treatment. There was a significant correlation between weeds plant population and the dry matter of potato, organic carbon percentage, soil specific weight and number of large potato tubers with potato tuber yield. Rye with common and triple plant density and barley with triple plant density compared to control increased tuber yield of potato 50, 33 and 35 percent, respectively. These treatments increased the number of large potato tuber 42, 33 and 27 percent, respectively compared with control.