In order to understand better the responses of rhizosphere bacterial diversity and organic carbon decomposition metabolism genes to tillage measures, rhizosphere soils of pumpkin rotated with wheat or watermelon were taken as test objects, and two nitrogen levels (N, 1.0 and 2.0 g/kg) were designed, the rhizosphere bacterial community structure and abundance of organic carbon decomposition metabolism genes were analyzed based on high-throughput sequencing technologies and PICRUSt analysis. The results showed that no significant difference was found in bacterial Shannon diversity index and community structure between different treatments. Proteobacteria, Bacterodidetes, Actinobacteria and Cyanobacteria were four dominant phyla in rhizosphere bacterial community structures under all treatments, with the sum of relative abundance reached 90%. Redundancy analysis showed that nitrate nitrogen in soils rotated with wheat, ammonium nitrogen and nitrate nitrogen in soils rotated with watermelon, played more important role in regulating bacterial community structure than those of other physiochemical indexes. At high nitrogen level, the relative abundance of Proteobacteria in soils rotated with wheat was lower than that in soils rotated with watermelon, but the relative abundance of Bacterodidetes and Actinobacteria was higher than that in soils rotated with watermelon (P<0.05). The abundances of enzymes gene expression such as α-amylase and β-galactosidase, important for the decomposition of hemicellulose and starch, were higher in soils rotated with wheat compared to that in soils rotated with watermelon. In conclusion, crop rotation and nitrogen application influence little on the microenvironment of pumpkin rhizosphere soil and the stability of bacterial community structure and diversity. At high nitrogen level, soil types rotated with different crops affect the relative abundance of bacterial phylum participating in organic carbon decomposition. The decomposition rate of organic carbon in soils rotated with wheat is higher than that in soils rotated with watermelon.