Mulching with straw and plastic film has been widely used to conserve soil water, increase temperatures, and increase crop yield in the dryland areas. However, its influence on soil nitrogen fractions is not well known. Based on a 7 year field experiment in the Weibei rainfed highland area of Loess Plateau of China, we compared the long-term effects of straw and plastic mulching on soil total nitrogen (STN), particulate organic nitrogen (PON), potential nitrogen mineralization (PNM), microbial biomass nitrogen (MBN), and mineral nitrogen (NO₃^--N and NH₄⁺-N) as well as on corn yield. Three treatments were included:no mulching, straw mulching, and plastic film mulching. Averaged across 5-7 years, the concentrations of STN, PON, PNM, MBN, and NO₃^--N at 0-10 cm depth increased by 13.11%, 64.29%, 17.51%, 16.94%, and 55.37%, and the STN, PON, MBN, and NO₃^--N concentrations at 10-20 cm increased by 5.93%, 33.33%, 15.78%, and 27.57% with straw than with no mulching (P < 0.05), respectively. The concentration of NO₃^--N increased by 189.14% and 135.75% at 0-10 and 10-20 cm in plastic film compared to no mulching (P < 0.05), respectively, and no significant differences in other fractions were found between plastic film and no mulching at both soil depths. Crop yield was improved by 6.90% and 36.74% in straw and plastic film mulching compared with no mulching (P < 0.05), respectively. Corn yield positively correlated with NO₃^--N and NO₃^--N/STN contents at 0-20 cm depths. Overall, straw mulching is favorable on soil N sequestration and could increase soil N activity and crop yield. However, N fertilizer should be applied during the late growing stage to maintain corn yield. Plastic mulching can effectively increase crop yield, but had no effect on soil total nitrogen, and its fractions and increased the risk of N leaching due to high NO₃^--N accumulation in the soil.