The experiment was designed to study the effects of continuous returning straw to maize filed on 0-40 cm soil nutrient and microbe,0-20 cm soil microbial biomass in 3-year returning(2007-2010),6-year returning(2005-2010),9-year returning(2002-2010),and non returning field at Pingliang maize breeding experimental station of Gansu agricultural university from 2002 to 2010.The tilth physical and chemical property and variation of main soil microorganism were tested to probe the effectiveness of continuous stra...