The research investigated the effect of seven crop rotation modes on cucumber rhizosphere bacterial community diversity by PCR-DGGE.The distinct bacterium in rhizosphere soil was classed as six population,they are Proteobacteria,SpHingobacteria,Flavobacteria,Actinobacteria,Clostridia and Acidobacteria.Flavobacteria was beneficial bacterium; it was rivalry bacterium to pathogenic bacterium of angular leaf spot.Most of Acidobacteria were pathogenic bacterium.Most of Clostridia were dispathopoiesis.Proteobacteria was major bacterial community in cucumber rhizosphere,it was infinite variety,including pathogenic bacterium and harmless bacterium.